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ON  CERTAIN   IMPROVED   PHOTOMETRIC  APPAR 
ATUS  AND  THE  RESULTS  THEREWITH 
OBTAINED. 


A  THESIS 

Submitted  to  the  Facultg  of  Cornell  University 
for  the  degree  of  Doctor  of  Philosophy 

bu 
CHARLES   PHILO  MATTHEWS 


f 

I   UN  TY  j 


ITHACA,  N.  Y. 
1901. 


ON  CERTAIN   IMPROVED    PHOTOMETRIC    APPARATUS  AND 
THE   RESULTS   THEREWITH   OBTAINED. 

The  material  in  the  following-  pages,  while  bearing  as  a  whole 
upon  the  general  subject  of  arc-light  photometry,  has  been  taken 
up  under  four  di&tinct  headings,  of  follows: 

I.  A  DEVICE  FOR  RECORDING  PHOTOMETER  SETTINGS. 

This  device  in  one  form  or  another  has  been  used  throughout 
all  the  experimental  work  of  which  description  is  given  hereafter. 

II.  THE   DOUBLE   MIRROR   METHOD   AND   ITS    APPLICA- 

TION TO  THE  STUDY  OF  COMMERCIAL  FORMS 
OF   THE  INCLOSED   ARC-LAMP. 

Following  a  description  of  the  method  and  certain  measure- 
ments to  determine  its  relative  accuracy,  will  be  found  the  experi- 
mental results  under  four  sub-headings,  .namely: 

1.  The    relative   value  of    different   makes    of    the   constant 
potential,  direct  current,  inclosed-arc  lamp. 

2.  The   relative    value    of    different   makes   of    the    constant 
potential,  alternating  current,  inclosed-arc  lamp. 

3.  A  report  on   the   relative  value  of  direct  and  alternating 
current  lamps. 

4.  An   investigation   of    the   coating   on   the  inner  globes  of 
inclosed-arc  lamps. 

III.  AN  IMPROVED  APPARATUS  FOR  ARC  LIGHT 

PHOTOMETRY. 


IV.    THE  LIFE  AND  EFFICIENCY  OF  COMMERCIAL-BRANDS 
OF  CARBONS  FOR  INCLOSED-ARCS. 

In  this  part  the  apparatus  described  in  part  III  has  been  used. 

19222:5 


PART  I. 

A  DEVICE  FOR  RECORDING  PHOTOMETER  SETTINGS. 


«F  THE 

({  UNIVERSITY   ) 

OF 


A  DEVICE  FOR  RECORDING  PHOTOMETER  SETTINGS. 
BY  CHARLES  P.  MATTHEWS. 

IN  the  ordinary  photometric  process,  there  occurs  between  successive 
settings  a  considerable  interval,  in  which  a  reading  of  the  bar  is 
taken  and  recorded,  either  by  the  observer  or  an  assistant.  Various  ex- 
pedients for  reading  the  bar  are  resorted  to,  as,  for  example,  the  use  of  a 
hand-mirror  to  reflect  a  beam  of  light  from  one  of  the  sources,  or  the 
turning  on  of  a  glow-lamp.  These  methods  are  not  free  from  objection. 
The  sudden  influx  of  light  produces  in  the  observer  fatigue  of  the  retina 
and  of  the  pupillary  muscles,  and  there  is  a  consequent  loss  of  visual  sen- 
sitiveness. Furthermore,  when  it  is  a  question  of  the  photometry  of  a 
fluctuating  source,  the  infrequency  and  irregularity  of  the  readings  is  a 
drawback.  In  arc -light  photometry  the  illumination  of  the  photometer 
disk  is  a  shifting  quantity.  Some  means  of  recording  a  setting  as  soon 


m? 


d 


Fig.  1. 

as  made,  thus  allowing  the  observer  to  proceed  to  a  subsequent  setting 
without  interruption  or  the  necessity  of  removing  his  gaze  from  the 
photometer  screen,  would  seem  likely  to  yield  more  satisfactory  results, 
with  a  considerable  economy  in  time. 


^  40 


CHARLES  P.    MATTHEWS. 


[VOL.  VII. 


In  the  course  of  experiments  on  the  alternating  arc  the  writer  has  used 
a  recording  drum  of  the  type  shown  in  Fig.  i.  A  cylinder  of  wood  10 
cm.  in  diameter  and  about  1.5  m.  in  length  is  mounted  with  its  axis 
parallel  to  and  somewhat  below  the  top  of  the  photometer  bar.  At  the 
end  of  a  spring  s,  attached  to  the  photometer  carriage,  a  steel  point  pro- 
jects downward  nearly  to  the  surface  of  the  cylinder.  A  rod '  r  extends 
the  length  of  the  cylinder  and  carries  at  one  end  a  pawl  which  engages 
the  teeth  of  a  ratchet  wheel  at  the  cylinder  end.  The  act  of  depressing 
sharply  the  rod  r  advances  the  cylinder  a  certain  angular  amount  and 
punctures  the  paper  by  means  of  the  steel  point  p, 

For  identifying  the  records  two  methods  suggest  themselves.  The 
point  p  may,  at  the  close  of  the  measurements,  be  placed  over  each 
puncture  successively  and  the  corresponding  reading  taken  from  the  bar, 
or  the  paper  covering  the  cylinder  may  be  ruled  and  marked  in  the  same 
manner  as  the  bar  itself,  when  the  settings  may  be  read  directly  from  the 
paper.  This  latter  has  the  advantage  of  making  a  permanent  record. 
It  is  not  necessary  to  have  the  cylinder  of  a  length  greater  than  \  to  f 
the  length  of  the  bar.  When  mounted  on  the  bar  in  the  manner  shown 
it  can  be  moved  so  as  to  accommodate  a  widely  fluctuating  series  of  read- 
ings. If  it  is  desired  to  refer  the  readings  to  time,  a  battery  circuit  may 
be  arranged  so  that  contact  between  the  rod 
r  and  the  spring  s  will  give  a  bell  signal. 
Two  additional  observers  are  then  necessary; 
one  to  call  and  one  to  record  time.  For  a 
single  observer  to  take  readings  referred  to 
time  the  drum  must  be  turned  at  a  known 
rate  by  means  of  a  clockwork.  This  is  not 
a  difficult  matter  to  arrange.  When  it  is 
desired  to  make  a  large  number  of  settings 
without  regard  to  their  sequence,  the  device 
may  be  used  with  the  pawl  lifted.  If  two 
impressions  of  the  point  are  superimposed 
the  appearance  of  the  puncture  usually  reveals 
the  fact. 

The  records  obtained  possess  the  natural 
advantages  peculiar  to  graphical  results. 
The  apparatus  lends  itself  admirably  to  the 
study  of  personal  error,  as  any  peculiarities 
are  at  once  manifest,  while  the  observer's  ig- 
norance of  his  settings  precludes  bias.  Some 
interesting  personal  records  have  been  ob- 
tained and  will  be  included  in  a  later  report. 
Fig.  2  is  a  record  of  20  settings  on  two  Fig.  2. 


No.  4.] 


PHOTOMETER   SETTINGS. 


241 


glow  lamps  placed  at  opposite  ends  of  the  bar  and  connected  in  parallel. 
Some  retinal  fatigue  is  shown  in  the  increasing  divergence  of  the  settings. 
Comparing  these  settings  with  20  settings  made  on  the  same  sources  but 
in  the  usual  way  we  find  : 

Probable  error  of  mean  without  recording  device  =  .173 
"  "     "     t(     with  "  "      =-i57 

These  preliminary  results  indicate  a  difference  of  about  10  %  in  favor  of 
the  mechanical  recorder. 

The  writer  has  successfully  used  this  device  in  the  study  of  the  alter- 
nating arc.  The  well-known  feature  of  the  arc  known  as  "hunting" 
produces  great  changes  in  its  luminous  intensity.  While  the  photometer 
is  peculiarly  an  instrument  requiring  deliberate  use,  one  can  nevertheless 
make  fairly  accurate  sittings  with  sufficient  rapidity  to  include  all  the 
major  fluctuations  in  this  light  source.  This  point  is  illustrated  in  Fig.  3. 


E" 


I   210 


ICO 


120 


Fig.  3. 

The   readings  occur,   on  an  average,   about  once    in    10    seconds.      A 
Krliss-Bunsen    photometer   was   used,  the  observer  standing   well   back 
from  the  screen.     It  would  doubtless  be  difficult,  if  not  impossible,  to  use 
the  Lummer-Brodhun  or  any  other  monocular  instrument  in  this  way. 
ELECTRICAL  LABORATORY,  PURDUE  UNIVERSITY,  June,  1898. 


PART  II. 


THE     DOUBLE    MIRROR    METHOD    IN    ARC-LIGHT     PHO- 
TOMETRY    AND     ITS    APPLICATION    TO  THE 
STUDY  OF    COMMERCIAL  FORMS  OF 
THE  INCLOSED  ARC  LAMP. 


In    a    paper  heretofore   published,*    I    have   sum- 
marized    the     causes     of    error    and    uncertainty     in 


*Trans    A.  I.  E.  E.  XV:599:] 


i6 

arc-light  photometry.  As  these  matters  are  patent 
enough  to  any  one  that  has  had  experience  in  such 
work,  I  will  not  go  into  a  detailed  recapitulation  of 
them  here,  except  in  so  far  as  a  description  of 
certain  methods  and  devices  intended  to  minimize 
such  errors  and  uncertainties  may  seem  to  necessitate. 
If  one  compares  the  results  obtained  by  different 
investigators  on  the  luminous  intensity  of  the  arc, 


FIG.  4. — PHOTOMETRIC  LABORATORY,  ADJUSTMENT   ROOM. 


he  finds  large  discrepancies.  Indeed,  so  discordant 
are  the  results  that  the  opinion  has  been  advanced 
by  some  that  such  measurements  are  almost  worth- 
less, and  that  any  attempt  to  obtain  consistent  and 
reliable  data  on  the  luminous  intensity  of  the  arc 
might  well  be  abandoned  at  the  outset.  This  is 
undoubtedly  an  extreme  view,  and,  personally,  I  do 
not  share  it.  We  have  to  consider  the  question : 


With  what  degree  of  accuracy  shall  we  be  content  ? 
Anything  comparable  with  the  accuracy  to  be 
obtained  in  purely  electrical  measurements  is  not 
to  be  thought  of.  On  the  other  hand,  that  the 
results  from  different  tests  should  be  concordant  to 
a  degree  no  better  than  fifty  per  cent  would  seem  to 
indicate  either  that  such  tests  have  been  made  under 


FIG.  5.     TYPES  OF  INNER  GLOBES. 


widely  different  conditions — that  is  to  say,  as  to 
carbons,  globes,  etc. — or  that  sufficient  time  and  study 
have  not  been  bestowed  on  the  methods  employed. 
I  am  of  the  opinion  that  an  absolute  accuracy  of  less 
than  ten  per  cent  and  a  relative  accuracy  in  any  one 
series  of  tests  of  less  than  five  per  cent  are  quite 
within  the  range  of  possibility. 

It  is  apparent  that  the   difficulties   met   in  the  pur- 


i8 

suit  of   good    results   in    arc-light    photometry  may  be 
classified  under  two  heads  : 

First — Those  peculiar  to  the  source,  and, 

Second — Those  peculiar  to  the  method. 

Of  the  first  class,  none  is  more  troublesome  than 
the  great  change  in  the  intensity  in  any  given  direc- 
tion, due  to  the  wandering  of  the  arc  over  the  surface 
of  the  carbon  tips.  For  instance,  if  the  arc  shifts 
suddenly  from  the  remote  side  of  the  carbons  to  the 
side  towards  the  photometer,  the  resulting  change  in 
luminous  intensity  may  be  200  per  cent.  Under  these 
circumstances,  the  only  hope  of  getting  a  value  rep- 
resenting the  mean  intensity,  at  least  with  the  use  of 
one  photometer  arranged  in  the  ordinary  way,  lies  in 
taking  a  relatively  great  number  of  readings  referred 
to  time,  and  in  integrating  the  result. 

To  accomplish  this,  I  have  employed,  and  described 
elsewhere,*  a  device  to  record  the  settings  mechanically. 
While  this  is  a  labor-saving  device,  it  does  not  obviate 
the  necessity  of  taking  many  settings,  nor  lessen  the 
number  of  computations.  Since  taking  up  the  work 
for  your  committee,  I  have  constructed  a  piece  of 
apparatus  that  greatly  reduces  the  fluctuation  in  the 
illumination  on  the  photometer  disc,  and  hence  gives 
a  good  result  with  a  greatly  diminished  number  of 
settings.  The  method  involved  may  be  well  designated 
as  the  double-mirror  method,  and  is,  so  far  as  I  know, 
new.f  It  consists  in  nothing  more  than  the  employ- 
ment of  two  mirrors  instead  of  one,  and  in  taking 
light  simultaneously  from  opposite  sides  of  the  arc  at 
the  same  inclination  to  the  vertical,  both  mirrors  being 

*  Physical  Review,  November,   1898. 

\  Since  writing  this,  I  find  that  the  eminent  French  photometrist, 
Blondel,  has  embodied  a  similar  principle  in  his  admirable  Photomesometre. 

C.   P.   M. 


'9 

capable  of  ready  adjustment  at  any  angle  in  the  ver- 
tical plane.  The  arrangement  of  apparatus  for  carrying 
out  this  plan  is  shown,  somewhat  diagrammatically,  in 
Figure  6. 

The  two  mirrors,  M,  M',  are  mounted  at  the  extrem- 
ities of  iron  arms,  and  are  suitably  counterbalanced, 
as  shown.  The  arc  is  fixed  in  the  center  of  rotation 
at  (a),  and  light  is  incident  upon  the  photometer  disc 
at  (c),  by  the  two  paths  shown  in  dotted  lines,  direct 
light  from  the  arc  being  cut  out  by  a  screen  not 
shown  in  the  figure.  This  plan  necessitates  a  fixed 
photometer,  P,  and,  in  order  that  a  variable  illumina- 
tion may  Be  produced  to  balance  that  due  to  the  arc, 
I  have  arranged  a  cord  and  windlass,  w,  permitting 
the  observer  to  move  with  facility  the  secondary 
standard,  s,  which  is  a  glow  lamp. 

At  D  is  shown  a  long  wooden  cylinder,  upon 
which  is  wrapped  the  paper  to  receive  the  records  of 
the  test.  These  records  are  made  by  an  electro- 
magnetic device,  R,  which  punctures  the  paper  when- 
ever an  electric  circuit  is  closed  at  the  button,  B. 

The  observer,  seated  before  the  photometer  in  a 
closely  screened  inclosure,  operating  with  one  hand 
the  windlass,  and  with  the  other  the  push-button, 
is  enabled  to  take  settings  with  relatively  great 
rapidity  and  accuracy.  At  a  point  200  cm.  to  the 
right  of  the  photometer  disc,  a  reserve  standard  is 
mounted  on  an  arm  that  may  be  swung  into  a  posi- 
tion in  line  with  the  bar.  This  reserve  standard  was 
carefully  evaluated  once  for  all  in  terms  of  the  Hefner 
lamp.  To  determine  the  intensity  of  the  secondary 
standard,  s,  it  is  only  necessary  to  turn  the  reserve 
into  position  and  record  a  series  of  readings  in  the 
same  way  as  for  the  arc.  This  operation  is  carried 
out  at  the  end  of  each  test,  or  more  frequently  if  any 


20 


21 


change  has  been  made  in  the  temporary  standard. 
Thus,  it  will  be  seen  that,  should  the  lamp  under  test 
be  found  particularly  weak  at  certain  angles,  the  limit 
of  the  bar  might  be  reached  in  the  attempt  to  get  a 
setting.  In  such  case,  it  is  necessary  to  stop  down 
the  temporary  standard  and  to  again  refer  it  to  the 
reserve.  I  may  add  that  the  reserve  is  never  allowed 
to  burn  more  than  a  few  minutes,  and  can  not  possi- 
bly deteriorate  under  such  conditions  of  use. 

With  this  disposition  of  the  mirrors,  the  angle  of 
incidence  at  the  photometer  disc  is  constant.  In 
Figure  6,  this  angle  is  shown  at  more  than  twice  its 
actual  value,  in  order  to  reduce  the  length  of  the 
drawing.  The  real  value  of  this  angle  is  5  degrees 
54  minutes.  To  make  a  correction  for  this  lack 
of  normal  incidence  would  mean  the  division  of 
the  intensities,  as  found,  by  the  cosine  of  5  degrees 
54  minutes,  or  .9947.  Failure  to  do  this  intro- 
duces an  error  of  about  one-half  of  one  per  cent, 
which  is  clearly  negligible  in  work  of  this  character. 

If,  at  a  given  instant,  i'  be  the  intensity  of  the 
arc  to  the  left,  and  i"  the  intensity  to  the  right,  d 
the  fixed  distance,  abc,  ds  the  distance  of  the  movable 
standard  and  K  the  mirror  coefficient,  we  have  as  the 
mean  intensity, 


i  +  r 


T     


I. 


s 
X   — 


K 


The  factor  in  the  bracket  was  computed  once  for 
all  for  values  of  d&  throughout  the  range  of  the  bar, 
and  these  values  were  laid  off  as  graduations  on  a 
long  T-square.  To  work  out  the  intensities  in  any 
particular  test,  it  suffices  to  pin  the  record  from  the 
drum  upon  a  long  table,  and  to  read  directly  from  a 


22 


T-square  the  values  of  the  bracketed  expression  corre- 
sponding to  the  punctures  in  the  paper.  The  mean 
of  these  values  for  any  one  position  multiplied  by  the 
factor  to  the  right  of  the  bracket  gives  the  intensity 
for  that  position  in  Hefner  units. 

It  is  of  course,  necessary  in  testing  sources  T*nth 
large  globes  or  shades  to  use  mirrors  of  such  size  that 
the  globe  or  shade  may  be  seen  in  its  entirety,  when 
the  eye  is  placed  at  the  point  c  (Figure  6);  and  it 
is  further  necessary  that  the  distance  abc  should  be 
large. 

It  is  important  to  note  that  the  double-mirror 
method,  while  enormously  diminishing  the  fluctuation 
due  to  wandering  of  the  arc,  can  have  no  effect  on 
such  fluctuations  as  are  due  to  variations  in  length  of 
the  arc,  or  to  variations  in  the  current  strength.  The 
relative  accuracy  of  the  single  and  double-mirror 
methods  will  be  brought  out  in  certain  data  to  be 
found  further  on. 

Of  the  difficulties  peculiar  to  the  method,  the 
most  serious  arises  from  the  attempt  to  compare  the 
arc  with  a  standard  of  different  color.  It  is  well 
known  that  when  the  color  difference  is  marked  the 
setting  partakes  of  the  nature  of  a  guess,  differing 
not  only  with  different  observers,  but  with  the  same 
observer  at  different  times.  To  minimize  the  error 
due  to  this  cause,  I  have  made  use  of  the  physiolog- 
ical fact  that,  as  the  illumination  of  two  surfaces 
tends  toward  zero,  the  eye  appreciates  their  difference 
in  color  to  a  less  and  less  degree,  and  is  thus  able 
to  estimate  an  equality  in  luminosity  unhampered  by 
the  sensation  of  color.  Thus,  the  method  of  winking, 
or  half-closing  the  eyes,  has  been  used  by  many 
experimenters  to  diminish  the  color  sensation.  These 
latter  processes  are  very  fatiguing  to  the  observer,  and 


23 

I  have  adopted  the  plan  of  diminishing  the  intensity 
of  the  photometric  field  by  the  use  of  a  rotating  sec- 
tored disc  E  (Figure  6)  of  very  small  angular  open- 
ing. Ferry  has  found  that  the  use  of  the  sectored 
disc  to  reduce  the  intensity  of  one  source  in  compar- 
ison with  another  of  different  color  introduces  an 
error,  because  the  ratio  of  the  light  transmitted  to 
light  cut  off  does  not  appear  to  be  the  ratio  of  the 
open  to  the  closed  sectors  when  the  opening  is 
small.  It  will  be  noted  that  the  disc  in  the  figure  is 
so  placed  as  to  diminish  equally  both  sides  of  the 
photometric  field,  and  hence  one  would  not  look  for 
an  error  of  this  character. 

To  test  the  accuracy  of  these  methods  with  dif- 
ferent observers,  I  operated  upon  an  automatic  feed, 
inclosed  arc  in  exactly  the  manner  that  has  prevailed 
throughout  the  tests,  and  requested  four  observers, 
whom  I  will  designate  by  S,  G,  K  and  F,  to  make 
nine  settings  each.  The  mean  results  are  : 

S  G  K  F 

813  808  852  845 

These  are  the  light  ratios  multiplied  by  a  constant. 
The  mean  of  all  is  830.  Hence,  the  individual 
means  differ  from  the  mean  of  all  by  : 

S  G  K  F 

-2%  -2.6$  +  2.6$  +  1.8$ 

As  these  settings  lay  in  nearly  the  same  range  on 
the  recording  drum,  I  inferred  that  a  part  of  the 
variation  was  due  to  an  insufficient  number  of 
settings. 

Subsequently,  observers  M  and  K,  who  have 
made  alL  the  settings  in  the  arc-light  tests  that 


UNIVERSITY 

CF 


follow,  took  a  greater  number  of  settings,  with  the 
following  results  : 

M   (16  settings)  K  (14  settings) 

7?o  775 

This  agreement  of  0.7  per  cent  is  so  close  that 
I  am  inclined  to  regard  it  as  somewhat  fortuitous, 
but  one  may  safely  conclude  that  the  error  due  to 
the  personal  equation  of  the  observer  is  little  greater 
when  this  method  is  used  than  it  is  in  the  comparison 
of  sources  of  like  color. 

As  to  the  error  due  to  fluctuation,  I  had  pre- 
viously taken,  by  the  single-mirror  method  and  the 
recording  drum,  seventy-one  settings  in  a  particular 
direction.  Taking  now  as  a  fluctuation  factor  the 
mean  deviation  from  mean  of  these  seventy-one  set- 
tings, and  disregarding  signs,  one  obtains 

Mean  intensity  x  a  constant =92  .9 

Fluctuation  factor  =29.6=:  32   per   cent. 

Maximum  deviation  —99     =106         " 

With  the  double-mirror  method  the  mean  of  the 
thirty  values  obtained  by  K  and  M  gives  : 

Mean  intensity  x  a  constant=772 

Fluctuation  factor  =  69.5=  9     percent. 

Maximum  deviation  =268     =34.7       " 

or,  in  a  word,  the  fluctuation  with  the  single-mirror 
method  is  more  than  thrice  that  with  the  double- 
mirror  method. 

UNITS 

The  values  of  luminous  intensity  in  these  tests 
are  expressed  in  terms  of  the  Hefner  amylacetate 
lamp.  They  may  be  reduced  to  British  candles  by 
multiplying  by  the  factor  .88.  I  would  call  attention, 


25 

however,  to  the  fact  that  this  is  little  more  than 
multiplying  by  an  arbitrary  constant,  since  ho  one 
knows  definitely  what  the  luminous  intensity  of  the 
British  candle  is.  On  the  other  hand,  the  Hefner 
unit  has  met  with  an  international  sanction,  and  is 
quite  generally  accepted  as  a  unit,  far  from  perfect, 
but  possessing,  especially  for  practical  purposes,  fewer 
faults  than  any  unit  thus  far  proposed. 


SPECIAL    TEST 

When  an  opalescent  inner  globe  is  used,  the 
globe  itself  becomes  more  or  less  luminous  by 
diffusion.  The  diffusion  differs  with  the  height  of 
the  arc  in  the  globe,  that  is  to  say,  with  the  length 
of  the  lower  carbon.  To  ascertain  the  magnitude  of 
this  effect,  I  have  carried  through  three  tests  on  the 
same  lamp  and  inner  globe,  and  also  the  same 
carbons,  the  lower  carbons  being  cut  successively  to 
the  lengths  four  and  three-quarter,  two  and  three- 
quarter  and  one  and  one-quarter  inches.  The  results 
appear  in  Table  i  and  Figure  7.  In  every  case  the 
arc  was  placed  at  the  center  of  the  mirror  system. 

An  inspection  of  these  results  shows  that  least 
light  is  obtained  with  the  arc  at  the  top  of  the 
globe,  and  most  light  when  the  arc  is  at  the 
mid-point.  This  is  explained  in  part  by  the  fact 
that  with  the  arc  at  the  top  a  good  part  of  the 
luminous  flux  is  incident  upon  the  non-reflecting 
surface  of  the  gas  cap. 

While  the  second  and  third  positions  yield  a  consid- 
erably increased  flux  of  light  with  a  clean  globe,  they 


26 


must  be  considered  as  impossible  conditions  in  prac- 
tice, since,  by  the  time  the  arc  has  descended  to  these 
points,  the  globe  has  received  a  coating.  The  net 
result  then,  as  the  lamp  burns,  is  due  to  an  increase 
in  light  flux  due  to  the  descending  arc,  and  a  dimi- 
nution in  light  flux  due  to  the  formation  of  a  coat- 
ing. How  this  affects  the  quantity  of  light  emitted— 

TABLE  i 

Special  test,  showing  effect  of  height  of  arc  in  globe 


Angle 

4%  inches 

aX  inches 

i^  inches 

59°  A 

61.3 

(55  A)    88.1 

50  A 

129.1 

122.2 

132.7 

40  A 

190.6 

209.4 

149.1 

30  A 

169.5 

214.6 

173-5 

20  A 

215.6 

273-5 

269.4 

10  A 

234-0 

265.1 

247.8 

Hor. 

215-5 

296.3 

252.3 

10  B 

277.8 

369-5 

372.3 

20    B 

291.7 

423.9 

388.5 

30  B 

382.4 

448.0 

365.9 

40  B 

354-6 

465-8 

435-1 

50  B 

264.3 

4O2.6 

353-3 

60  B 

263. 

329. 

278.1 

70  B 

202.9 

243-5 

197.3 

80  B 

3.64 

36.9 

Globes 

•- 

Opalescent  Inner  Only 

Mean     hemispherical, 

UDoer 

178  H    U 

199  H    U 

185  H    U 

Mean     hemispherical, 

lower             

288  H    U 

385  H    U 

-3CT      H         TJ 

Mean  spherical  

233  H.  U. 

292  H    U 

268  H    U 

time     integrated 
is  a    subject    for 


that    is,    the    product    of    flux    and 
throughout    the    life  of  the  carbons- 
future    investigation,    and    involves    the    questions    of 
carbons,  shape  of  globe,  etc. 

In  the  tests  that  follow,  I  have  chosen  the  initial 
condition  as  the  simplest  to  obtain,  even  though  the 
light  emitted  may  be  less  than  at  some  subsequent 
period  in  the  life  of  the  carbons. 


Should  any  one  desire  to  test  a  lamp  for  the  pur- 
pose of  obtaining  comparative  results,  he  would  not 
be  under  the  necessity  of  burning  the  lamp  for  many 


FIG.  7. — VARIATION  OF  LUMINOUS  INTENSITY  WITH   HEIGHT  OF  ARC  IN  A 
CLEAN    OPALESCENT  GLOBE. 

Curve  I.— Lower  Carbon,  4^  in.     Curve  II.— Lower  Carbon,  2%  in.     Curve   III.— Lower 

Carbon,   i%  in. 

hours  to  get  the  proper  conditions,  as  he  would 
necessarily  have  to  do  were  one  of  the  lower  positions 
chosen  in  these  tests. 


28 


FIRST    INVESTIGATION 

In  order  to  determine  the  status  of  the  direct- 
current,  inclosed  arc  as  found  commercially  on  the 
market,  it  seemed  desirable  to  study  first  the  ques- 
tions of  luminous  intensity,  power  consumption  and 
efficiency,  taking  the  lamps  as  supplied  by  the  makers, 
but  operating  under  a  certain  uniformity  in  conditions. 
These  conditions  are 

1.  The  same  brand  of  carbons  throughout. 

2.  An    opalescent    or    milky    inner    globe,    and    a 
clear  outer,  as  supplied. 

3.  An    opalescent    inner    globe,    and    an     "opal," 
ground,  or  milky  outer  globe,  as  supplied. 

To  these,  I  have  added  in  certain  cases  a  test  with 
no  outer  globe  whatever,  in  order  that  the  absolute, 
as  well  as  the  relative,  absorption  of  the  outer  globes 
might  be  found. 

The  lamps  are  fitted  with  the  proper  lengths  of 
carbons,  and  adjusted,  as  nearly  as  possible,  to  the 
voltage  at  the  arc  named  in  the  makers'  specifications. 
They  are  then  allowed  to'  burn  until  thoroughly  heated 
before  the  test  begins.  One  observer  maintains  the 
terminal  electro-motive  force  constant,  and  takes  read- 
ings of  the  current  throughout  the  test,  while  another 
operates  the  photometer.  The  values  of  current  given 
are  therefore  the  mean  of  many  readings. 

From  the  records  taken  off  the  recording  drum 
the  values  in  the  tables  are  computed.  These  values 
are  then  plotted  in  polar  co-ordinates,  as  shown  in 
the  curves  below,  and  also  in  rectangular  co-ordinates 
in  the  well-known  Rousseau  diagram,  which  latter  is 
integrated  by  the  planimeter  to  get  the  mean  spherical 
intensity. 

In  this  way  eight  direct-current,  no-volt  lamps 
have  been  tested  up  to  the  present  writing. 


29 

Referring  to  the  lamps  by  number  we  find  the 
results  on  Lamp  i  in  Table  2,  Figure  8. 

The  curves  show  very  clearly  the  slight  absorption 
of  the  clear  outer  and  the  large  absorption  of  the 
opalescent  outer.  The  clear  outer  globe  shows  some 
diffusion,  as  it  tends  to  round  out  the  curve.  Thus 


TABLE  2 

LAMP  i 


Angle 

Test  i 

Test  2 

Test  3 

59°  A 

109.8 

50  A 

140.3 

35- 

(45  A)     54.9 

40  A 

162.6 

85.3 

87.2 

30  A 

169.7 

137-7 

159-5 

20  A 

178.5 

207.9 

223.9 

10  A 

218.1 

246.4 

270.2 

Hor. 

190.9 

259- 

253.2 

10  B 

178.3 

282.1 

334-7 

20    B 

214.67 

370.7 

400.1 

30  B 

191.7 

401.6 

454-3 

40  B 

188.2 

404-3 

432.1 

50  B 

209.3 

346.1 

387-1 

60  B 

134.4 

308. 

307.1 

70  B 

114.1 

177-8 

303-3 

80  B 

175-2 

264.7 

101.3 

Globes 

Op  Inner 
Op.  Outer 

Op.  Inner 
Clear  Outer 

Op.  Inner 
No  Outer 

E    M    F        

no  volts 

no  volts 

no  volts 

Current 

4  87  amperes 

5  07  amperes 

5  08  amperes 

Watts 

tf'ie  7 

cc7  7 

«8  8 

Mean  hemispherical  / 

Upper,  159.5 

137-5 

149.9 

intensity                     f 

Lower    186  4 

OT2  2 

^62  4. 

Mean  spherical  intens- 

itv 

172  O 

214  8 

256  I 

Watts  per  mean  H.  U. 

3  10 

2-37 

2.18 

there  are  two  regions  where  curve  II  extends  beyond 
curve  III.  In  the  case  of  the  opalescent  outer  globe, 
the  diffusion  is  so  marked  that  the  luminous  intensity 
is  practically  constant  throughout  a  very  large  solid 
angle.  In  the  higher  angles  above  the  horizontal,  the 
intensity  is  greatly'  increased,  producing  the  effect, 
approximately,  of  aluminous  sphere  of  equal  intrinsic 


3° 


brightness.  This  results  in  the  elimination  of  shadows, 
and  the  production  of  a  pleasing  light  for  interiors. 
The  quality  of  light  is  also  changed  to  a  considerable 


FIG.  8. — LAMP  i. 

Curve  I.— Opalescent  Outer  Globe.     Curve  II. -Clear  Outer  Globe.     Curve  III.— No 

Outer  Globe. 

extent  through  the  absorption  of  the  excess  of  violet 
rays  otherwise  very  marked  in  the  light  of  the  arc. 
This  result  is  attained,  however,  at  a  diminished 


efficiency.  In  this  and  nearly  all  the  curves  with  the 
opalescent  outer  globes,  a  certain  wavy  outline  is 
noticed.  I  think  this  effect  is  due,  in  large  part,  to 
the  variations  in  the  diffusive  power  of  the  globe 
itself.  One  finds  difference  in  thickness  and  trans- 
lucency  to  a  considerable  extent  in  such  globes,  and, 

TABLE  3 

LAMP  3 


Angle 

Test  i 

Test  2 

59°  A 

(5  5  A)           59-5 

87.3 

50 

102.7 

114  7 

40 

153-7 

it>5.3 

30 

164.2 

182.8 

20 

203.8 

198.1 

10 

209.3 

206.2 

Hor. 

219.8 

222.8 

10  B 

262.7 

239-2 

20 

273.1 

232.6 

30 

328.7 

2I9.J 

40 

364.1 

241.4 

50 

315.5 

282.1 

60 

224.8 

227. 

70 

288.6 

185.7 

80 

IIO.2 

165.8 

Globes 

Op.  Inner 
Clear  Outer 

Op.  Inner 
Op.  Outer 

E    M    F 

no  volts 

no  volts 

Current 

5.1  amperes 

c    amoeres 

Watts  

561. 

CCQ 

Mean  hemispherical  in-  / 

Upper,   150. 

D  D*-** 

160. 

tensity  H    U          .  .    .  f 

Lower,  282. 

27O 

Mean  spherical  H.  U.  .  .  . 
Watts  per  mean  spherical 

216. 
2.60 

&yj. 

195. 

2.85 

as  the  angle  of   view  changes,  these  differences  would 
tend  to  distort  the  distribution  curve. 

In  Table  3  and  Figure  9  are  the  results  of  two 
tests  with  the  usual  combination  of  globes  on  lamp  3. 
In  this  case  the  opalescent  globe  transfers  a  certain 
portion  of  the  luminous  flux  to  the  upper  hemisphere 
—sufficient,  in  fact,  to  throw  curve  II  quite  out  to 
the  curve  obtained  with  the  clear  globe. 


32 


Following  are  the  data  and  curves  of  a  test  on 
lamp  4.  This  lamp  is  provided  with  an  outer  globe 
of  ground  glass.  The  inner  globe  has  straight  walls, 


FIG.  9. — LAMP  3. 

Curve  I. — Opalescent  Innei',  Clear  Outer.    Curve  II. — Opalescent  Inner,  Opalescent  Outer. 

and  with  the  arc  at  the  top  the  distribution  curve 
comes  out  somewhat  oddly.  The  luminous  flux 
above  the  horizon  is  very  small.  The  strong  intensity 
at  eighty  degrees  below  with  the  clear  outer  globe 


33 

has  been  found  in  more  than  one  case  under  like 
conditions.  I  have  not  been  able,  thus  far,  to  arrive 
at  a  satisfactory  explanation  of  it,  but  it  seems  to  be 
associated  in  some  way  with  a  multiple  reflection 
due  to  the  outer  globe.  Professor  Thomas  has  found 
similar  strong  changes  in  intensity  in  the  case  of  the 


TABLE  4 

LAMP  4 


Angle 

Test  i 

Test  2 

59°  A 

50 

39-5 

40 

52.6 

30 

81. 

28.3 

2O 

107.2 

80.4 

IO 

136.7 

167.6 

Hor. 

145-2 

213.4 

10   B 

185-5 

231.9 

20 

199-5 

235. 

30 

185-3 

219-9 

40 

199. 

208.9 

50 

140.3 

175-8 

60 

143.4 

176.3 

70 

192. 

168.8 

80  t 

104.2 

190.5 

Globes 

Op.  Inner 
Ground  Outer 

Op.  Inner 
Clear  Outer 

E    M    F       

no  volts 

HO  volts 

4.76  amperes 

4.76  amperes 

Watts              

523.6 

523.6 

Mean  hemispherical  in-  / 
tensity  in  H.  U  f 

Upper,     80.4 
Lower,  173.6 

70.4 

208. 

Mean  spherical  H.  U.  .  .  . 
Watts  per  mean  spherical 

127. 
4.12 

139.2 
3.76 

slow  lamp,  due  to  images  of  the  filament,  whose 
effect  becomes  very  marked  at  certain  angles.  It 
may  be  that  we  have  a  similar  phenomenon  here. 

In  figures  n,  12,  13,  14  and  15  are  found  the 
curves  taken  on  lamps  5,  7,  9,  10  and  12  respectively. 
The  corresponding  tables  are  5,  6,  7,  8  and  9.  These 
tests  are  made  under  the  conditions  already  specified. 


34 


The  curves  differ  in  detail,  but  show  similar  character- 
istics. In  considering  them,  one  should  remember 
that  while  the  lamps  have  nominally  outer  globes  of 


FIG.  10. — LAMP  4. 

Curve  I. — Ground  Outer  Globe.     Curve  II. — Clear  Outer  Globe. 

the  same  kind,  they  have  markedly  different  inner 
globes.  Again,  some  of  the  lamps  have  a  bright 
metallic  surface  above  the  inner  globe.  This  surface 


35 

acts  to  some  extent  as  a  reflector.  Taking  these 
facts  into  consideration  in  connection  with  the  varia- 
tions in  the  transparency  of  different  parts  of  any 
one  outer  globe,  one  can  understand  why  these  curves 
do  not  more  closely  follow  a  general  type. 


TABLE  5 

LAMP  5 

.   Angle 

Test  i 

Test  2 

59"  A 

91.9 

II4-5 

50 

IIO.4 

M0.5 

40 

II4.7 

134-9 

30 

157-9 

166.7 

20 

154-5 

163.1 

IO 

162.2 

177.6 

Hor. 

1  60.0 

169.1 

10   B 

206.4 

176.2 

20 

274.6 

165-5 

30 

256.4 

179.5 

40 

263.8 

168.9 

50 

225.3 

162.7 

60 

212.3 

162.7 

70 

IO5.2 

157.2 

80 

144.7 

157-2 

Globes 

Op.  Inner 
Clear  Outer 

Op.  Inner 
Op.  Outer 

E    M    F 

no  volts 

no  volts 

Current 

4  16  amperes 

4.16  amperes 

Watts       

457.6 

457.6 

Mean  hemispherical  in-  ) 
tensity  in  H    U     .  .  .  .  C 

Upper,   126.6 
Lower,  220.8 

141.6 
167.2 

Mean  spherical  H.  U.  .  .  . 

173-7 

154-4 

Watts  per  mean  spherical 

H    U      

2.63 

2.96 

I  will  leave  further  discussion  of  the  curves  show- 
ing distribution  of  luminous  intensity  until  the  second 
and  third  divisions  of  this  subject,  as  outlined  by 
your  committee,  have  been  taken  up,  and  pass  to  other 
matters  in  a  resume*  of  the  results  of  the  first  inves- 
tigation. At  a  common  terminal  electro-motive  force 
of  no  volts,  seven  of  these  lamps  take  an  average  cur- 
rent of  4.90  amperes,  which  means  an  average  total 


36 

power  consumption  in  each  lamp  of  539  watts.     With 
80  volts    at    the    arc    this    power    is    divided    into   147 


Fiu.  ii. — LAMP  5. 
Curve  I.— Clear  Outer  Globe.      Curve  II.— Opalescent  Outer  Globe. 

watts  waste  in  the  resistance  coils  and  392  watts  in 
the  arc.  The  average  yield  of  light,  expressed  as 
mean  spherical  intensity,  is  : 


37 

Opalescent  inner,  no  outer*  =256  H.  U. 

"      clear  outer  =207  H.  U. 

"  "      opalescent  outer  =177  H.  U. 


TABLE  6 

LAMP  7 


Angle 

Test  i 

Test  2 

Test  3 

60°  A 

"3-7 

50 

49-9 

104.9 

145  8 

40 

65.6 

135.2 

157-6 

30 

103.3 

164.7 

183.7 

20 

150.2 

167.9 

194.2 

IO 

135-4 

231.7 

218.7 

Hor. 

182.7 

256.5 

215-1 

10    B 

i9J-3 

299.2 

251-9 

20 

225.7 

313. 

242.5 

30 

237-4 

357-6 

234-9 

40 

236.8 

407.9 

238.6 

50 

195.6 

403.5 

234.2 

60 

173-4 

235- 

220.  6 

70 

142.3 

173.4 

193-4 

80 

63.3 

197.9 

237. 

Globes 

Op.  Inner 
Coated.  Clear  Outer 

Op.  Inner 
Clear  Outer 

Op.  Inner 
Op.  Outer. 

E.  M    F  

IIO  volts 

IIO  volts 

IIO  volts 

Current 

4  76  amperes 

4  66  amperes 

4  87  amperes 

Watts  .            .    . 

C2^  6 

ei2  6 

e  -ic   7 

Mean  hemispherical  ) 

Upper,    96. 

149. 

175- 

intensity,  H.  U...  ] 

Lower,  200. 

316.8 

232. 

Mean  spherical,  H.  U. 

•      148. 

232.9 

203.5 

Watts  per  mean  spher- 

ical, H.  U  

*.54 

2.  2O 

2.63 

Hence  the  power  required  to  produce  one  unit  of 
light  in  this  type  of  lamp  is 

Opalescent  inner,  no  outer*  —2. TO  watts. 

u  "      clear  outer  =2.66  watts. 

"  "      opalescent  outer     =3. 04  watts. 


*The  computations  for  no  outer  globe  have  not  the  same  value  as  the 
others,  for  the  reason  that  the  number  of  such  tests  was  less. 


38 

In  conclusion,    I   would    call    attention    to    the    fact 
that  these  figures  give  the  value  of  this  type  of  lamp 


FIG.  12. — LAMP  7. 

Curve  II. — Clear  Outer  Globe.     Curve  III. — Opalescent  Outer  Globe. 


as  a  light  producer,  and  not  as  a  light  distributor. 
The  efficiency  of  the  type  as  a  distributor  of  light 
can  best  be  found  from  a  consideration  of  the  curves 


39 


of  illumination — a    matter  that  does    not    form   a    part 
of  this  investigation. 


SECOND    INVESTIGATION 


As    furnishing     data    on     the    luminous     intensity, 
power  consumption    and    efficiency  of    the    alternating- 


TABLE  7 

LAMP  9 


Angle 

Test  i 

Test  2 

55°A 

126.5 

91.8 

5o 

153.6 

IlS.o 

40 

189.1 

168.7 

30 

188.4 

184.1 

20 

2II.5 

243.5 

10 

211.3 

220.2 

Hor. 

209.4 

247.6 

10    B 

231.4 

323.9 

20 

206.9 

301.6 

30 

217.0 

313.3 

40 

181.4 

294.0 

50 

158.0 

253-5 

60 

165.5 

214  I 

70 

136.5 

254-7 

80 

156.4 

no. 

Op.  Inner 

On.  Inner 

Globes 

Op.  Outer 

Clear  Outer 

E    M    F     

no  volts 

no  volts 

Current 

4  79  amperes 

4.9  amperes 

Watts                  

526.9 

t-iq. 

Mean  hemispherical  in-  / 

Upper,   170.4 

171.2 

tensity   H    U     f 

Lower    194  4 

28l   2 

Mean  spherical,  H.  U. 

182.4 

226.2 

Watts  per  mean  spherical 

H    U          

2.83 

2.-?8 

current,  inclosed  arc  lamp  for  constant-potential  cir- 
cuits, I  give  below  the  results  of  tests  on  seven 
lamps.  These  tests  have  been  carried  through  under 
conditions  identical  with  those  prevailing  in  the  first 
investigation.  In  two  cases  the  lamps  were  accom- 


4o 


panied  by  shades,  and  these  lamps  were  subjected  to 
additional  tests  to  bring  out  the  advantages  of  using 
a  shade  on  an  alternating-current  lamp. 


FIG.  13. — LAMP  9. 

Curve  I.— Opalescent  Outer  Globe.     Curve  II.— Clear  Outer  Globe. 


The  lamps  are  adjusted  for  voltage  at  the  arc,  and 
for  the  frequency  of    the   supply,   which    is    60    cycles. 


After  burning  a  sufficient  time,  they  are  tested  in  the 
manner  already  described. 

Since  lamps  of  this  type  are  used  with  one  cored 
and  one  solid  carbon,  some  difference  in  the  curve  of 
distribution  might  be  looked  for  as  a  result  of  using 


TABLE  8 


LAMP  10 


Angle 

Test  i 

Test  2 

5Q°A 

(5  5  A)          no.  i 

50 

125.7 

82.7 

40 

129.7 

177.7 

30 

188.1 

198.7 

2O 

219.  6 

230. 

IO 

264.1 

268.2 

Hor. 

246.8 

247. 

10  B 

239-6 

279.7 

20 

230.7 

370.7 

30 

293.6 

399-2 

40 

244.1 

353-5 

50 

210.7 

254.2 

60 

215-9 

277.7 

70 

135.9 

279.2 

80 

154- 

121.5 

Globes 

Op.  Inner 
Op.  Outer 

Op.  Inner 
Clear  Outer 

E    M    F  

1  10  volts 

1  10  volt*5 

Current  

5  05  amperes 

4  94  amperes 

Watts       ... 

555  5 

C.A'l  A 

Mean  hemispherical  in-  ) 

Upper,   173.6 

176. 

tensity    H   U                 \ 

Lower    230  8 

308  8 

Mean  spherical  H.  U.  .  .  . 

202.2 

242.4 

Watts  per  mean  spherical 

H   U 

2  71 

2  2J. 

the  cored  carbon  above  and  the  solid  one  below,  or 
vice  versa.  In  Table  n  and  Figure  1 6  will  be  found 
the  results  of  two  tests  intended  to  give  information 
on  this  point.  Lamp  102  was  tested  under  the  usual 
conditions  of  an  opalescent  inner  and  a  clear  outer 
globe,  the  cored  carbon  being  below.  Some  days 


later    the    lamp  was  tested  with    the  same   globes,   but 
with  the  carbon  pencils  interchanged,  the  upper  pencil 


|100  120   140  1160   180   200 


I  Opalescent  Outer, 


FIG.  14. — LAMP  10. 

Curve  I.— Opalescent  Outer  Globe.     Curve  II.— Clear  Outer  Globe. 


being    the    cored    one.     The   globe  was  clean   in    both 
cases.      It  will    be    noted    that    the  curves    follow  each 


43 

other  closely,  particularly  below  the  horizontal.  The 
slight  variations  in  the  curves  neutralize  each  other  so 
that  the  mean  spherical  intensity  comes  out  the  same 
in  both  cases.  It  is  to  be  concluded  from  this  test 
that  the  reversal  of  the  carbons,  which  takes  place 


TABLE  9 

LAMP  12 


Angle 

Test  2 

Test  4 

Tests 

54°  A 

116.9 

50 

134.8 

6l.I 

78.4 

40 

169.8 

126.9 

129.2 

30 

I7I.2 

2II.9 

138.4 

20 

176.4 

236.3 

154-2 

10 

190.9 

253-0 

162.3 

Hor. 

219.8 

239-9 

186.1 

10  B 

228.0 

247.8 

241.9 

20 

214.8 

282.3 

236.3 

30 

198.3 

269.8 

208.2 

40 

189.1 

236.7 

209.2 

50 

175-0 

195-3 

185-  T 

60 

171.9 

173.2 

I5I.5 

•70 

137-9 

168.4 

176.7 

80 

251.5 

84.0 

150.3 

Globes 

Op.  Inner 
Op.  Outer 

Op.  Inner 
Clear  Outer 

Op.  Inner 
Coated.    Clear  Outer 

E   M    F    

no  volts 

no  volts 

no  volts 

Current 

40^  amperes 

4T\  amperes 

4  74  amperes 

Watts               

•  V«2             r 

542.3 

'iO  ***i-1f^i  ^^ 

520.  3 

if.,  j  L^  MBMgn»*«* 

c>21.4 

Mean  hemispherical  [ 

Upper,  154.4 

3"^ft  J 
1  60. 

O           *T^ 

120.8 

intensity,  H.  U.  ..  \ 

Lower,  200.8 

230.4 

204.8 

Mean  spherical  H.  U. 

177.6 

195-2 

162.8 

Watts  per  mean  spher- 

ical H    U 

-7    (X 

2.66 

3  2O 

J'^J 

j*  *•*-* 

whenever  the  lamp  is  newly  trimmed,  makes  but  little 
difference  in  the  total  luminous  flux  from  the  lamp. 
However,  in  the  tests  reported  below,  the  uniform 
practice  of  a  cored  lower  carbon  was  kept  to. 

Table  12    and    Figure   17  exhibit   the   results   of   a 
test    on    lamp    101.      These    might    be    taken    for    the 


44 


curves    from    a    direct-current    lamp,    so    small    is    the 
luminous    flux  in  the  upper  hemisphere.      It  must  be 


FIG.  15. — LAMP  12. 

Curve  II.— Opalescent  Outer  Globe.     Curve  IV.— Clear  Outer  Globe. 


remembered,  however,  that  the  arc  is  at  the  top  of 
the  globe,  as  already  explained,  and  much  of  the 
upward  light  is  either  absorbed  or  reflected  by  the 


45 

comparatively    broad    surfaces    just    above    the    inner 
globe. 

The  maximum  intensity  is  found  in  its  usual 
position,  thirty  degrees  below.  The  opalescent  outer 
globe  shows  the  usual  diffusive  properties. 


TABLE  10 


LAMP  12 


Angle 

Test  i 

Test  3 

54°A 

76.9 

50 

77-7 

72.6 

40 

123.2 

163.0 

30 

140.9 

228.9 

20 

150.8 

259- 

10 

I55-I 

276.6 

Hor. 

169.8 

3I4-I 

10   B 

165.1 

343-9 

20 

166.7 

3I4-I 

30 

195.6 

300.8 

40 

167.8 

255-3 

50 

175.9 

258.3 

60 

176.2 

207.8 

70 

2IO.3 

87.3 

80 

169.6 

197.2 

Globes 

Op.  Inner 
Coated.  Clear  Outer 

Op.  Inner 
Clear  Outer 

E    M    F                             .. 

no  volts 

no  volts 

Current       

4.98  amperes 

4.97  amperes 

Watts 

ej.7  g 

£46  7 

Mean  hemispherical  in-  \ 

D*t/'  u 

Upper,  125.4 

Jt^*  / 
185.6 

tensity   H   U                 ) 

Lower    176.8 

28l.2 

Mean  spherical  H.  U.  .  .  . 

'   151.1 

233-4 

Watts  per  mean  spherical 

H    U    . 

T.  62 

2-1.1 

J.  \J£, 

•J-+ 

Three  tests  on  lamp  102  have  been  carried  out. 
The  highly  beneficial  effect  of  a  shade  is  here  well 
shown.  (Figure  18.)  With  the  arc  at  the  top  of 
the  globe,  the  shade  in  this  case  received  all  the 
upward  flux  of  light  and  a  portion  of  the  downward 
flux.  The  result  is  that  the  horizontal  intensity  is 


46 

diminished,    but    below    ten    degrees    B    the    result    of 
substituting    a    shade    for    an    outer     globe     is     very 


FIG.  16. — LAMP  102. 

Curve  I.— Clear  Outer,  Lower  Carbon  Cored.     Curve  IV.— Clear  Outer,  Upper  Carbon 

Cored. 


beneficial.      In   fact,   the    mean    hemispherical    intensity 
with   shade   bears   to   that   with    clear   outer   globe    the 


47 

ratio  266  :  236,  or  an  increase  of  nearly  thirteen 
per  cent.  Taking  a  similar  ratio  with  reference  to 
the  opalescent  outer  globe,  one  finds  266  :  165,  or  an 
increase  of  sixty-one  per  cent.  As  the  arc  burns 
lower,  the  intensities  between  the  horizontal  and 


TABLE   ii 


Angle 

Test  i 

Test  4 

55°A 

66.1 

57-3 

50 

96.1 

97-3 

40 

170.9 

152.2 

30 

215.7 

195.3 

20 

223.6 

227-5 

10 

225.9 

252.2 

Hor. 

249.8 

256.0 

10  B 

259.8 

253.3 

20 

270.4 

270.8 

30 

270.7 

265.2 

40 

256.5 

251-9 

50 

220.8 

229.7 

60 

184.8 

174.0 

70 

IOO  I 

93-8 

80 

72.6 

81.4 

Globes 

Op.  Inner 
Clear  Outer 

Op.  Inner 
Clear  Outer 

EMF       

no  volts 

i  io  volts 

Current  

6.81  amperes 

6.80  amperes 

App   Watts 

7J.Q  I 

7J.8 

Watts  

I'vj'  • 

A  en 

/4°- 
478 

Power  Factor  

4OV" 

.61 

T-/  u" 

6-? 

Mean  hemispherical  in-  } 
tensity  in  H.  U  f 
Mean  spherical  in  H.  U.. 

Upper,   169.4 
Lower,  236.5 
202.9 

•          •  ^'  J 

169.4 
234.6 

202. 

Watts  per  mean  H.  U.  .  .  . 

2.26 

2.36 

ten  degrees  B  will  naturally  be  strengthened,  because 
the  arc  will  no  longer  be  eclipsed  by  the  shade.  At 
the  same  time  the  intensities  in  all  directions  will 
be  increased,  for  the  reasons  already  discussed  in 
connection  with  Figure  7.  For  the  illumination  of 
points  remote  from  the  arc  it  is  better  that  the  solid 


48 

angle    subtended    by    the    shade    should     not    exceed 
27t  steradians,  as  it  does  in  the  case  here  represented. 


40     60    180    MOO    120    140\   1CO    180    200 


FIG.   17. — LAMP  101. 
Curve  I. — Clear  Outer  Globe.     Curve  II. — Opalescent  Outer  Globe. 

It  will  further  be  noted  that  there  is  an  abundance 
of  light  at  all  points  beneath  the  lamp,  both  with 
shade  and  with  opalescent  outer  globe. 


49 


Figure  19  (see  Table  14)  shows  the  results  on  a 
lamp  fitted  with  an  inner  globe  having  straight  side 
walls.  The  curve  is  very  strong  in  the  horizontal 
and  falls  off  at  all  angles,  both  above  and  below. 


TABLE  12 


LAMP  101 


Angle 

Test  i 

Test  2 

55°A 

54-2 

5o 

58.6 

40 

33-5 

79-4 

3o 

42.4 

122. 

20 

127.0 

128.7 

10 

154.3 

137-4 

Hor. 

185.0 

•       149.2 

10   B 

186.2 

165.2 

20 

213.0 

175-7 

30 

239-3 

160.0 

40 

223.1 

164.7 

50 

206.8 

152.9 

60 

200.0 

137.6 

70 

igi.O 

123.0 

80 

149.8 

82.8 

Globes 

Op.  Inner 
Clear  Outer 

Op.,  Inner 
Op.  Outer 

E    M.  F  

no  volts 

Current  

6  47  amperes 

Watts  app  

711   7 

Watts 

AA& 

097.4 

A/tf\ 

Power  factor.  .  .  . 

62 

440. 
61 

Mean  hemispherical  in-  ) 
tensity    H    U                C 

Upper,     76.7 

•**3 

97-5 

T  ef\ 

Mean  spherical,  H.  U.  .  .  . 

141.1 

150. 
126.7 

Watts  per  mean  spherical, 

H.  U  

-1/ 

3>52 

Whether  or  not  this  effect  is  associated  with  the 
shape  of  this  type  of  globe,  I  dare  not  say  without 
further  investigation,  but  the  matter  can  be  settled 
definitely  when  the  tests  on  inner  globes  of  different 
shapes  are  carried  out. 


Another  lamp  having  a  shade  is   106.       (Table   16, 
Figure  21.)     The  shade  in  this  case  extends  downward 


FIG.  18. — LAMP  102. 
Curve  I.— Clear  Outer  Globe.    Curve  II.— Opalescent  Outer  Globe.    Curve  III.— Shade. 

to  a  plane  about  a  half-inch  above  the  arc,  when  the  latter 
is  at  its  highest  point.  The  horizontal  intensity  with 
shade  is  slightly  less  than  with  clear  outer  globe, 


showing  that  the  latter  strengthens  this  intensity  by 
diffusion  more  than  it  reduces  by  absorption.  The 
increase  in  intensity  from  the  horizontal  to  twenty 
degrees  B  is  very  marked  when  the  shade  is  employed 


TABLE  1 3 

LAMP  102 


Angle 

Test  i 

Test  2 

Test  3 

59°A 

77-6 

55 

66.1 

1  06.  6 

5o 

96.1 

116.7 

94.6 

40 

170.9 

123.9 

95-o 

30 

215-7 

139-9 

86.8 

20 

223.6 

160.7 

84.2 

10 

225.9 

159.6 

86.1 

Hor. 

249.8 

165.6 

124.1 

10  B 

259.8 

204.4 

245-3 

20 

270.4 

176.3 

3I7-3 

.  30 

270.7 

161.1 

322.6 

40 

256.5 

161.1 

304.6 

50 

220.8 

154.3 

280.2 

60 

184.8 

144-8 

258.6 

70 

1  06.  1 

125-5 

2366 

80 

72.6 

112.  6 

186.7 

Globes 

Op.  Inner 
Clear  Outer 

Op.  Inner                      Op.  Inner 
Op.  Outer                           Shade 

E.  M.  F  

no  volts 

no  volts 

no  volts 

Current 

6  81  amperes 

6  78  amperes 

6  77  ampere^ 

App  watts  

740.  i 

745.8 

744  7 

Watts 

Atin 

48^ 

jc  7 

Power  factor  
Mean  hemispherical  / 
intensity  in  H.  U.  } 
Mean  spherical  in  H.  U. 
Watts  per  mean  spher- 
ical in  H.  U...  

.61 

Upper,  169.4 
Lower,  236.5 
202.9 

2  26 

.64 
127.2 
164.8 
146. 

3  "31 

.61 

85.2 
266.4 

175-8 

2  60 

in  the  position  here  indicated,  and  these  are  angles  of 
most  importance  in  street  lighting,  if  not  in  interiors. 
The  mean  hemispherical  intensity  is  altered  by  the 
substitution  of  the  shade  for  the  clear  outer  globe  in 
the  ratio  of  254:169  or  fifty  per  cent  as  against 


*J 

thirteen    per    cent    in    the    case    of    lamp    102.       It     is 
worth  noting  that    the   curvature  of   the  two  shades  is 


FIG.  19.— LAMP  103. 
Curve  I.— Ground  Outer  Globe.    Curve  II.— Clear  Outer  Globe. 


opposite — that  of    106    being    such    as   to  reflect    light 
incident  at  high  angles,  so  as  to  make  it  useful,  while 


53 


that  of  102  throws  light  incident  at  angles  higher 
than  about  twenty-five  degrees  A  upwards,  where  it 
is,  in  a  large  measure,  dissipated  by  multiple  reflection 
and  absorption.  This  fact  accounts,  I  think,  for  the 


Angle 


TABLE    14 

LAMP  103 


Test 


Test  2 


SO°A 

59-8 

50  7 

40 

98.0 

IOI.6- 

30 

108.0 

140.3 

20 

133-6 

153-9 

10 

145-8 

174-7 

Hor. 

156.9 

180.2 

10  B 

I45-I 

179.2 

20 

147.4 

172.2 

3° 

150.3 

169.1 

40 

136  5 

152.3 

50 

123.6 

136  5 

60 

99.4 

96.0 

70 

IOI.O 

59-8 

80 

89.9 

47  3 

Globes 

Op.  Inner 
Ground  Outer 

Op.  Inner 
Clear  Outer 

E    M    F 

no  volts 

1  1  o  vol  ts 

Current  

5.91  amperes 

5.87  ampere*^ 

App    watts 

650.  i 

f\\C    "7 

Watts     

424. 

^*rS    / 
4IO 

Power  factor  

•r*"r' 

65 

^.iu. 
61 

Mean  hemispherical  in-  (_ 

•  ^Z) 

Upper,    98.2 

•  wj 
113- 

tensity  in  H    U  \ 

Lower,  133.2 

146  8 

Mean  spherical  in   H.  U. 

II5-7 

129.9 

Watts  per  mean  spherical, 

H    U 

i  66 

3T  d 

j-uu 

•  lo 

great  difference  in  these  two  examples  of  the  employ- 
ment of  a  shade.  The  low,  flat  shade,  concave  inwards, 
is  certainly  superior  optically,  if  not  artistically. 

As  to  the  efficiency  of  this  type  of  lamp,  we  have 
in  Table  19  a  recapitulation  of  the  power  measure- 
ments in  the  alternating-current  lamps.  The  mean 


54 

power    consumption    of    seven    lamps     is    417    watts. 
The  average  value  of  the  mean  spherical   intensity  is 

With  clear  outer  globe,  159  H.  U. 

"      opalescent  outer  globe,    130  H.  U. 


FIG.  20. — LAMP  105. 

Curve  I.— Opalescent  Outer  Globe.     Curve  III.— Clear  Outer  Globe. 


55 

Therefore,    as     light    producers,    the    average     effi- 
ciency is  : 

With  clear  outer  globe,  2.62 

"      opalescent  outer  globe,  3.21 

in  watts  per  mean  spherical  Hefner  unit.  The  mean 
power  in  the  arc  is  342  watts,  and  in  the  mechanism 
74  watts. 


TABLE  15 

LAMP  105 


Angle 

Test  i 

Test  3 

59°A 

99.9 

55 

50 

124.0 

109.3 

40 

129.0 

157-8 

30 

149.1 

I77-I 

20 

150.4 

205.7 

10 

146.3 

211.  2 

Hor. 

153-4 

211.  2 

10  B 

142.2 

228.3 

20 

I28.I 

236.6 

30 

137.6 

244.6 

40 

121.  0 

236.1 

50 

IO7.O 

23I.I 

60 

120.6 

202.9 

70 

I25.I 

134-9 

80 

77.0 

I3I-I 

Globes 

Op.  Inner 
Op.  Outer 

Op.   Inner 
Clear  Outer 

E   M    F 

IIO  volts 

IIO  volts 

Current 

6.21  amperes 

6.19  amperes 

App    watts  

68^  r1 

68O  Q 

Watts 

WJ,  J. 

Aid 

\JW.  \J 

4.IO 

Power  factor     .... 

ifj-^.. 
.60 

if.  J.  W. 

.60 

Mean  hemispherical  in-  ) 

Upper,  128.4 

154-8 

tensity  in  H.  U  ) 

Lower,  127.3 

218.8 

Mean  spherical  in  H.  U.. 

127.8 

186.8 

Watts  per  mean  spherical 

in  H    U 

-3  24 

2.20 

Jj.  ^T- 

FIG.  21. — LAMP  106. 
Curve  I.— Clear  Outer  Globe.     Curve  II.— Opalescent  Outer  Globe.     Curve  III.— Shade. 


57 


TABLE  16 

LAMP  106 


Angle 

Test  i 

Test  2 

Test  3 

55°A 

59-9 

39-5 

122.9 

50 

90.8 

40.1 

129.2 

40 

139-1 

44.0 

152.4 

30 

164.9 

36.8 

147-3 

20 

163.7 

46.7 

152.6 

10 

189.7 

79.0 

149.4 

Hor. 

179.9 

174.9 

159.0 

10  B 

191.9 

251.9 

158.4 

20 

196.4 

276.2 

145-7 

30 

188.0 

268.4 

143-3 

40 

177.7 

269.1 

117  2 

50 

140.7 

244.8 

98.2 

60 

136.5 

293.6 

95-2 

70 

108.1 

186.6 

109.9 

80 

63.4 

272.5 

103.8 

Globes 

Op.  Inner 
Clear  Outer 

Op.  Inner 
Shade 

Op.  Inner 
Op.  Outer 

E    M    F         

no  volts 

no  volts 

no  volts 

Current 

6.1  amperes 

6.  i   amperes 

6.17  amperes 

App    watts             .    ... 

671 

671 

678  7 

Watts 

\j  y  A  . 
<5Q2 

W  f  A  . 

-378 

/       •  / 

?7I 

Power  Factor  

Jy*" 

•58 

J/u. 
.56 

3  I  A  • 

•54 

Mean  hemispherical  / 

Upper,   136.8 

49.6 

132.8 

intensity  in  H.  U.  f 

Lower,  169.5 

254-4 

130.4 

MeansphericalinH.U. 

I53-I 

152. 

131.6 

Watts  per  mean  spher- 

ical in  H.  U  

2  c6 

2  4.Q 

2.82 

••  3^ 

***TTF 

FIG.  22. — LAMP  108. 

Curve  I.— Clear  Outer  Globe.    Curve  It.— Opalescent  Outer  Globe. 


59 


TABLE   17 

LAMP  1 08 


Angle 

Test  i 

Test  2 

Test  3 

55°A 

82.9 

s2.2 

5o 

55-3 

80.9 

III.  2 

40 

105.1 

130.7 

186.6 

3o 

159.0 

116.5 

2I6.I 

20 

210.7 

134-5 

220.5 

TO 

206.0 

163.3 

217.9 

Hor. 

225.1 

I5I-9 

183.2 

10  B 

234-4 

160.5 

219.0 

20 

229.4 

153-3 

249.2 

30 

239.1 

142.9 

279.1 

40 

222.6 

156.7 

279-3 

50 

215.8 

137-7 

224.4 

60 

150.2 

162.9 

204.7 

70 

143.0 

150.9 

231.7 

80 

52.6 

121.  1 

I5I.2 

Globes 

Op.  Inner 
Clear  Outer 

Op.  Inner 
Op.  Outer 

Op.  Inner 
Coated.  Clear  Outer 

E.  M.  F  

no  volts 

1  10  volts 

1  10  volts 

Current  

6.56  amperes 

6.47  amperes 

6.41  amperes 

App    watts     

721  6 

711   7 

7o<  I 

Watts 

/  ^ 

4C7   e 

/  A  A  .  y 

44.O 

/  WD  *  A 
J.62 

Power  factor. 

H-D  /  •  D 
.63 

*T4TV-'» 
.6l 

v»« 

6=; 

Mean  hemispherical  ( 

Upper,   139.9 

II5-9 

•  wj 
167-5 

intensity  in  H.  U.  j 

Lower,  211.2 

150.4 

233-7 

Mean  spherical,  H.  U. 

175-5 

I33-I 

200.  6 

Watts  per  mean  spher- 

ical   H    U 

2.61 

•7    -5Q 

*           2  ^O 

J*  J^J 

««  J1-1 

00 


FIG.  23. — LAMP  no. 

Curve  I.— Clear  Outer  Globe.    Curve  II.— No  Outer  Globe. 


6i 


TABLE  18 


LAMP  no 


Angle 

Test  i    . 

Test  2 

45  A 

80.4 

66.4 

40 

106.6 

132.9 

30 

144.2 

157  2 

20 

146.2 

149.4 

10 

162.6 

176.4 

Hor. 

103-3 

165.2 

10  B 

176.2 

184.7 

20 

192  8 

187.6 

30 

168.7 

192.0 

40 

147.2 

164.7 

50 

128.7 

148.4 

60 

105.5 

126.3 

70 

98.6 

55  3 

80 

36.5 

70.4 

Globes 

Op.  Inner 
Clear  Outer 

Op.  Inner 
No  Outer 

E.  M.  F     

no  volts 

no  volts 

Current 

6  07  amperes 

6  3  amperes 

App    watts  

667  7 

603 

Watts  

33Q. 

338. 

Power  factor 

CQ 

48 

Mean  hemispherical  in-  / 

Upper,   109.6 

118.4 

tensity  in  H    U              C 

Lower    143  2 

161  6 

Mean  spherical  in   H.  U 

126.4 

140. 

Watts  per  mean  spherical 

in  H.  U.. 

2.68 

2.41 

TABLE  19 

POWER  MEASUREMENTS 


Toul 

In  Arc 

Mechanism 

Lamp  No. 

101  
IO2  

448 
•  .  4^0 

340 

375 

108 

84 

n    i 

IO^ 

424 

*IAA 

80 

ii    i 

io«; 

414 

382 

32 

ti    t 

106  
108 

378 

4^7 

298 
383 

80 

74 

• 

no  

33Q 

276 

63 

62 

THIRD — A    REPORT    ON    THE    RELATIVE    VALUE    OF    DIRECT 
AND    ALTERNATING-CURRENT    LAMPS. 

The  lamps  used  in  the  two  foregoing  investiga- 
tions, considered  as  types,  are  unfortunately  not  of 
the  same  power  consumption,  but  regarding  t  ic-m 
merely  as  light  producers,  the  average  direct-current 
lamp  yields,  with  opalescent  inner  and  a  clear  outer 
globe,  207  h.  u.,  whereas  the  average  alternating-cur- 
rent lamp  for  circuits  of  the  same  pressure  yields  159 
h.  u.,  which  gives  the  former  lamp  an  advantage  as 
a  light  source,  irrespective  of  efficiency,  in  the  ratio 
of  48:159  or  thirty  per  cent.  It  is  pretty  well  dem- 
onstrated that  the  alternating  arc  is  per  se  less  effi- 
cient than  the  direct-current  arc.  Just  what  the  proper 
ratio  may  be  is  a  matter  for  physical  research,  and 
varies  with  several  factors,  such  as  current  density, 
wave  form,  character  of  the  circuit,  etc.  We  have 
no  data  in  these  investigations  to  furnish  reliable 
information  on  this  point,  as  there  are  too  many  vari- 
able conditions  met  in  the  lamps  as  found  in  their 
commercial  form. 

Comparing   the  average  performance  of    the  lamps 
in   the  first   series  of   tests  with    the  average  perform- 
ance of   the  lamps    in    the  second  series  of    tests,  one 
finds    very    nearly    the    same    power  consumption    per, 
light  unit,  namely : 

.  D.  c.  A.  c. 

Clear  outer 2.60  2.62 

Opalescent  outer.. 3. 04  3.21 

This  result  differs  from  one  that  I  have  formerly 
published,  which  shows  the  direct-current  lamp,  as  a 
result  of  a  single  comparison  as  superior  in  economy 
to  the  other  type.  I  consider  the  combined  result  of 


63 

these  tests  as  of  far  greater  value  than  the  result  of 
the  single  comparison.  Moreover,  a  considerable 
improvement  in  the  alternating-current  lamp  has 
doubtless  taken  place  in  the  last  two  years,  whereby 
its  economy,  as  well  as  its  operation,  are  found  to  be 
bettered. 

Question  of  design,  steadiness  of  operation,  carbon 
consumption,  etc.,  are  purposely  left  out  of  this  com- 
parison until  such  time  as  more  data  shall  be  available. 

To  compare  the  direct-current  lamp  with  the  alter- 
nating-current lamp  on  the  basis  of  mean  spherical 
intensity  is  not  always  fair.  When  a  diffusing  outer 
globe  is  used,  this  basis  of  comparison  is  correct 
enough,  for  the  reason  that  the  distribution  of  intensity 
is  fairly  constant  in  all  directions,  both  for  the  direct 
and  alternating-current  types. 

For  outdoor  use,  however,  lamps  will  be  provided 
with  inner  globes  only,  or  clear  outer  globes,  or 
shades,  as  the  case  may  be.  In  any  event,  the  upward 
luminous  flux  which  passes  the  globes  or  shades  is 
practically  of  no  utility.  Hence  for  outdoor  use  the 
mean  hemispherical  intensity  below  a  plane  passing 
through  the  arc  is  a  better  basis  for  comparison. 

Now,  the  average  direct-current  lamp  in  this  series 
of  tests  yields  a  mean  hemispherical  intensity  of  273 
*h.  u.  with  clear  outer  globe.  The  average  alternating- 
current  lamp  yields  but  190  h.  u.  This  gives  the 
former  an  advantage  as  a  useful  light  source  repre- 
sented by  the  ratio  of  83:190,  or  43.7  per  cent. 
Moreover,  the  power  required  per  unit  intensity  is  in 
the  two  cases  1.97  watts  and  2.19  watts  per  mean 
hemispherical  h.  u.,  so  that  not  only  does  the  direct- 
current  lamp  with  clear  outer  globe  give  a  stronger 
mean  intensity  below  the  arc,  but  it  does  so  at  a 
higher  efficiency.  But  it  is  wasteful  to  use  an  alter- 


64 

nating-current  lamp  for  street  lighting  without  a  shade 
or  reflector.  The  tests  on  lamps  102  and  106  enable 
one  to  draw  certain  interesting  comparisons.  They 
give  mean  hemispherical  intensities  respectively  of  266 
and  254  h.  u.,  or  very  nearly  the  same  as  the  average 
direct-current  lamp  with  clear  outer.  This  yield  is 
obtained  at  a  power  consumption  of  only  418  watts, 
which  is  i. 6 1  watts  per  h.  u.  This  emphasizes  the 
great  importance  of  a  shade  on  the  alternating-current 
lamp.  Finally,  we  may  compare  this  last  result  with 
the  performance  of  direct-current  lamp  i,  with  no 
outer  globe  and  no  shade.  Here  the  mean  hemi- 
spherical intensity  is  362  h.  u.,  the  power  consump- 
tion 558  watts  and  the  power  per  h.  u.  1.54  watts. 
The  conclusion,  based  on  this  single  comparison,  is 
that  for  street  lighting  the  55<>watt  (nominal  rating) 
direct-current  lamp  without  shade  gives  39  per  cent 
more  useful  light  than  the  45o-watt  (nominal  rating) 
alternating-current  lamp  with  shade  and  at  slightly 
greater  economy. 

But  the  fact  must  not  be  lost  sight  of  that  this 
last  comparison  is  between  constant  potential  inclosed 
arcs  as  found  on  the  market.  The  question  of  the 
light  output  and  efficiency  of  the  series  alternating 
inclosed  arc  of  the  same  power  as  the  direct-current 
lamp  will  be  taken  up  later. 

Table  20  gives  a  summary  of  the  results  in  the 
two  foregoing  investigations.  I  have  also  plotted 
(Figure  24)  what  may  be  termed  a  composite  curve 
for  each  type.  These  curves  are  nothing  more  than 
means  of  the  foregoing  individual  curves  for  a  clear 
outer  globe.  The  irregularities  due  to  differences  in 
globes,  reflecting  surfaces,  and  other  causes  are  found 
to  largely  neutralize  each  other  with  the  result  of  the 
smooth  loci  here  shown.  These  two  curves  will  be 


65 

TABLE  20. 


Watts  Consumed. 

Mean  Intensity 
inH.  U. 

Mean  Watts. 

a. 

| 

c 
G 

u 

Spherical. 

w   ,  "rt 

Spherical  H.  U. 

N| 

U 

U 

In  Lamp. 

In  Arc. 

Mechan- 

•3*f 

^H 

Op. 

Clear 

Clear 

Op. 

Clear 

Clear 

Outer 

Outer 

Outer 

Outer 

Outer 

Outer 

I 

5-OI 

551 

401 

150 

I72 

235 
2^6* 

332 
362* 

3.10 

2-37 
2.18* 

.66 

3 

5.08 

559 

406 

152 

195 

216 

282 

2.85 

2.6o 

•99 

4 

4.76 

524 

381 

143 

127 

139 

208 

4.12 

3-76 

•52 

5 

4.i6f 

458 

333 

125 

174 

221 

2.96 

2.63 

.07 

7 

4.76 

524 

38i 

143 

203 

333 

317 

2.63 

2.20 

•65 

9 

4.84 

532 

387 

145 

182 

226 

28l 

2.83 

2.38 

.89 

10 

4-99 

549 

399 

150 

202 

242 

309 

2.74 

2.24 

•77 

12 

4-87 

536 

390 

146 

I78 

195 

230 

3-05 

2.66 

2-33 

Mean 

4-9 

529 

384 

144 

I76 

207 

272 

3-03 

2.60 

1.98 

A.  C. 
Lamp. 

Hie 

££2 

°£< 

101 

6.40 

448 

•  63 

340 

.  82 

108 

127 

141 

206 

352 

317 

2.17 

102 

6.79 

459 

.61 

375 

-73 

84 

146 

203 
I76f 

236 

266f 

3-31 

226 
26of 

1.94 

103 

5-89 

424 

•  65 

344 

•75 

80 

116 

130 

147 

3.66 

3-15 

2.88 

105 

6.20 

414 

.61 

382 

.80 

32 

128 

187 

219 

3-24 

2.20 

1.89 

1  06 

6.12 

378 

•  56 

298 

.70 

80 

132 

153 

169 

2.82 

2.56 

2-49t 

2.23 
i.48f 

1  08 

6.48 

457 

.64 

383 

.80 

74-5 

133 

175 

211 

3-30 

2.61 

2.16 

no 

6.18 

339 

•49 

276 

•72 

63 

140* 

126 

143 

2.4I* 

2.68 

2-37 

Mean 

6.29 

417 

.60 

342 

.76 

74-5 

130 

159     190 

3-31 

2.66 

2.23 

*  Condition  of  no  outer  globe.         f  Condition  with  shade  on  Lamp. 
NOTE — All  marked  values  not  included  in  the  mean. 

found  valuable  for  the   plotting  of  curves  of  illumina- 
tion. 

Absorption  of  Globes  : 

The  results  of  the  first  and  second  investigations 
enable  one  to  obtain  some  interesting  figures  on  the 
absorption  of  the  outer  globes.  It  is  evident  that  if 
we  take  the  mean  spherical  intensity  of  any  lamp  with 
a  clear  outer  globe,  and  divide  it  by  the  intensity 


66 


obtained  with  no  outer  globe,  we  get  a  ratio  that 
show  the  transmission  of  the  clear  globe.  I  am  able 
to  get  this  ratio  in  three  cases.  The  values  are  91.7, 


to' 


FIG.  24. 


90.3  and  88.8.  The  mean  of  these  is  90.2.  In  other 
words,  a  clear  globe  cuts  down  the  luminous  flux 
from  the  inner  globe  by  about  ten  per  cent.  In  a 


67 
% 

similar  way  two  opalescent  globes  were  found  to 
produce  an  absorption  of  21.8  and  32.4  per  cent,  or  a 
mean  of  27.1  per  cent.  These  figures  give  what  may 
be  termed  the  absolute  absorption  of  the  clear  and 
opalescent  globes.  We  may  also  find  the  relative 
transmission  (understanding  the  term  transmission  in 
a  very  general  sense,  that  is  to  say,  having  in  mind 
both  diffusion  and  absorption)  of  the  opalescent  and 
clear  outer  globes  by  taking  the  ratio  of  the  cor- 
responding mean  spherical  intensities.  Following  are 
the  values:  73.6,  90.3,  91.3,  88.9,  87.2,  80.7,  83.9, 
91.,  89.8,  72.,  89.1,  69.4,  86.,  75.8.  The  mean  of  the 
values  is  83.5.  It  will  be  noted  that  there  is  a  wide 
variation  in  these  figures,  the  lowest  being  69.4  and 
the  highest  91.3.  To  "look  at  the  matter  in  another 
way,  if  we  substract  each  one  of  these  values  from 
100,  we  have  a  series  of  numbers  that  represent  the 
diminution  in  mean  spherical  intensity  resulting  from 
the  substitution  of  an  opalescent  globe  for  a  clear 
globe  in  each  case.  The  wide  variations  might  have 
been  predicted  from  a  casual  examination  of  the 
globes  as  sent  by  the  manufacturers.  Herein  lies  one 
large  factor  of  uncertainty  in  determining  the  relative 
lighting  value  of  different  makes  of  inclosed  arc  lamps. 


FOUR     AND     FIVE INVESTIGATIONS    ON    THE     COATING    OF 

THE    INNER    GLOBE. 

As  regards  the  work  called  for  under  these  head- 
ings, I  am  unable  to  do  more  at  this  date  than  to 
give  the  results  of  certain  tests  and  experiments 
undertaken  tentatively  with  a  view  of  getting  at  the 
best  method  of  procedure.  Attention  has  already 
been  called  to  the  fact  that  the  change  in  the  inten- 
sity of  an  arc-lamp  with  the  burning  away  of  the 


68 

carbons  is  due  principally,  if  not  entirely,  to  two 
factors,  one  of  which  is  the  coating  formed  on  the 
inner  globe.  It  becomes  important  to  know  the 
time-law  of  formation  of  this  coating.  To  this  end, 
several  lamps,  of  both  the  direct  and  alternating- 
current  types,  were  fitted  with  carbons  and  started  on 
a  time  run.  At  intervals,  the  inner  globes  were 
removed  and  tested  photometrically  for  absorption  by 
placing  inside  of  them  a  slender  incandescent  lamp 
maintained  at  constant  intensity.  It  is  not  to  be 
expected  that  the  total  absorption  of  such  globes  can 
be  independent  of  the  distribution  of  luminous  inten- 
sity about  the  source  within  the  globe.  That  is,  the 
actual  absorption  with  the  glow  lamp  is  likely  to  be 
different  from  that  with  the  arc,  yet  the  change  in 
the  absorption  as  the  coating  forms  could  not,  it  was 
thought,  differ  to  any  marked  extent  with  the  nature 
of  the  source.  The  results  of  these  tests  have  not,  as 
a  rule,  been  very  satisfactory,  owing  to  a  variety  of 
complications  which  I  need  not  here  discuss.  How- 
ever, certain  interesting  points  are  made  manifest  from 
a  consideration  of  the  most  uniform  of  these  results. 
If  we  reduce  the  various  intensities  from  the  glow 
lamp  at  different  angles  to  unity  by  dividing  intensities 
in  any  given  direction  by  the  initial  intensity  in  that 
direction,  we  have  the  effect  of  a  source  giving  a 
uniform  light  in  all  directions.  The  falling  of  the 
intensities  at  different  angles  with  time  in  the  case  of 
a  direct-current  lamp  is  shown  in  Figure  25,  wherein 
the  dotted  lines  represent  the  change  in  intensity  at 
different  angles,  and  the  full  curve  the  change  in 
mean  spherical  intensity.  The  upper  set  of  curves  is 
for  the  angles  above  the  horizontal ;  the  lower  set  for 
the  angles  below  the  horizontal.  The  curves  show 
clearly  that  the  coating  forms  most  heavily  on  the 


69 

upper  part  of  the  globe,  a  fact  which  is  apparent 
from  the  appearance  of  the  globe.  A  fact  which  is 
not  so  apparent,  but  one  which  the  curves  bring  out 


60  80 

TIME  IN  HOURS 
FIG.  25. 


clearly,  is  that  the  coating  forms  very  rapidly  at  first 
and  then  gradually  decreases  in  rate  of  formation,  or, 
to  be  more  accurate,  the  absorption  of  light  changes 


in    this    way.       It    will  be    noted  that  the  mean    hemi- 
spherical intensity  falls  from    100  to  64  in   100    hours. 


.100 


IOQ 


\\ 


\\ 


10  * 


20* 


60 


30  /» 


/0 


4O  5"O  60 

///  Hours. 


FIG.  26. 


Below  the  horizontal,  the  falling  off  in  the  same  time 
is  from    100  to   76. 

Figure  26   shows  the   formation   of    the  coating   in 


7' 

the  case  of  an  alternating  lamp  during  a  period  of 
forty  hours.  Here  again  the  coating  forms  most 
rapidly  above  the  horizontal. 

In  the  case  of  four  alternating  lamps  the  inner 
globes  were  weighed  at  intervals.  When  these  weights 
are  plotted  against  time  we  have  the'  set  of  curves  in 
Figure  27,  extending  from  the  origin  upwards.  Unlike 


12- 


•6/0 

%> 

•59 

C 


24 


£**=* 


04- 


^ 


20 


. 
Hours. 


FIG.  27. 


the  absorption  curves,  these  loci  show  an  increasing 
rate  of  deposit  with  the  life  of  the  lamp.  It  is  not 
to  be  expected  that  the  increase  in  the  mass  of  the 
deposit  and  in  the  amount  of  light  cut  off  by  the 
deposit  should  follow  the  same  law.  It  seems  reason- 
able that  successive  equal  increments  of  coating  might 
cut  off  diminishing  increments  of  light,  and  the  trend 
of  the  curves  seems  to  indicate  this  clearly. 


72 


Tt  was  not  intended  to  take  up  the  matter  of  carbon 
life  until  a  thorough  study  of  the  matter  could  be 
made  apart  from  other  things.  However,  as  the 


/4 


^x 


XNx 


s 


20 


40 


60  30 

Js/rie  Jf 

FIG.  28. 


100 

Hours. 


iao 


weights  of  the  carbons  were  taken  at  intervals  during 
the  runs  made  for  the  sake  of  the  coating,  I  am  able 
to  plot  certain  curves  of  carbon  consumption  which 


73 


may  be  indicative  of  what  may  be  found  under  a 
more  extended  investigation.  The  upper  and  lower 
carbon  life  curves  of  four  alternating-current  lamps 


FIG.  29. 

appear  in  Figure  27.  There  seems  to  be  a  tendency 
for  the  carbons  to  burn  more  rapidly  towards  the  end 
of  the  life.  This  corresponds  to  the  upward  tendency 


74 

to  be  noticed  in  all  the  weights  of  coating,  except 
one.  The  life  of  the  lamps,  on  one  trimming,  is  in 
the  vicinity  of  seventy  hours.  Lamp  102  cut  out  in 
47.5  hours  because  of  the  rapid  combustion  of  the 
upper  carbon — the  lower  carbon  being  still  quite  long. 
There  may  have  been  some  abnormal  conditions  in 
this  case  unknown  to  the  observers. 

Figure  28  shows  a  similar  set  of  curves  for  four 
direct-current  lamps.  Lamp  7  failed  to  cut  itself  out 
and  the  bottom  of  the  globe  was  fused.  This  accounts 
for  the  sudden  drop  in  the  curve  of  the  lower  carbon. 
Of  these  lamps,  number  5  shows  the  longest  life,  the 
run  not  having  terminated  when  the  last  measurement 
was  made.  Here,  again,  we  note  the  accelerated 
combustion  toward  the  end. 

I  am  able,  at  this  time,  to  give  the  results  of  some 
initial  and  final  tests  which  bring  out  the  joint  effect 
of  the  coating  and  the  descending  arc.  Thus  Figure  29 
shows  an  initial  and  final  test  on  lamp  12  (see  table  9, 
tests  4  and  5).  The  absorption  in  this  case  is  16.4 
per  cent,  after  106  hours.  Another  brand  of  carbons 
in  this  lamp  gives  the  results  found  in  table  10.  One 
notes  here  a  considerably  higher  initial  intensity,  but, 
on  the  other  hand,  a  much  heavier  coating,  the  final 
absorption  after  105  hours  being  35.2  per  cent.  This 
lamp  was  fitted  with  an  inner  globe  of  the  closed 
bottom  type.  The  other  type  of  inner  globe  presents 
less  surface  for  the  reception  of  the  ash,  and  one 
would  look  for  a  larger  light  absorption  at  the  end 
of  the  carbon  life.  A  preliminary  test  on  lamp  7 
(see  table  6)  shows  that  the  loss  in  intensity  at  the 
end  of  the  life  was  36.5  per  cent. 

In  Figure  30,  which  represents  the  result  of  a 
coating  test  on  an  alternating-current  lamp,  one  finds 
the  striking  result  of  more  light  with  coating  than 


75 


without.     (See  table   17.)     The  absorption  is  14.3  per 
cent.      It  is  important  here  to  remember  that,  with  the 


0' 


So' 


SO' 


6.0* 


FIG.  30. 


arc  at  the  top,  the  strong  upper  lobe  of  the  distribu- 
tion curve  of  the  alternating  arc  is  very  much  cur- 
tailed. Now,  as  the  arc  lowers,  this  lobe  unfolds,  as 


it  were.  In  seventy  hours'  time  the  coating  has  not 
formed  with  sufficient  rapidity  to  offset  this  increase 
in  luminous  flux.  Hence  the  result  shown. 


©F   THE 

UNIVERSITY 

CF 


PART  III. 


AN  IMPROVED    APPARATUS     FOR   ARC-LIGHT 
PHOTOMETRY. 


A  paper  presented  at  the  i$()th  Meeting  of 
the  American  Institute  of  Electrical  Engin- 
eers, New  York)  September  27 th,  IQOI. 


[ADVANCE  COPY  SUBJECT  TO  REVISION.] 

AN  IMPROVED  APPARATUS  FOR  ARC-LIGHT 
PHOTOMETRY. 


BY    CHARLES    P.  MATTHEWS. 


The  usual  process  in  arc-light  photometry  involves  the  deter- 
mination of  the  distribution  curve  of  luminous  intensity  in  a 
vertical  plane  through  the  axis  of  the  carbons,  and  the  subse- 
quent integration  of  a  derived  curve  in  rectangular  co-ordinates 
(the  Rousseau  diagram).1  The  ordinate  of  this  latter  curve  is 
the  measured  intensity,  and  the  increment  of  the  abscissa  is  pro- 
portional to  the  area  of  the  elementary  zone  which  such  intensity 
illuminates  of  an  imaginary  sphere  about  the  source.  The  mean 
ordinate  of  this  derived  curve  is  the  value  sought.  Under  the 
most  favorable  conditions  this  task  is  a  tedious  one,  several  hours 
being  usually  required  for  its  completion. 

Methods  designed  to  shorten  this  process,  through  the  pro- 
duction upon  the  photometer  screen  of  an  illumination  propor- 
tional to  either  the  mean  spherical  or  mean  hemispherical  in- 
tensity of  the  source  are  not  new.  Of  these  integrating  methods, 
the  writer  is  aware  of  two  due  to  Blondel,2  and  one  due  to 
Houston  and  Kennelly.3 

Unfortunately,  two  of  these  methods  are  adapted  only  to  the 
photometry  of  the  open  arc,  while  the  third,  although  worked 

1.  See  Appendix. 

2.  The  Lumenmtftre.     U Edairage    Klectrique,   March,  April,  May,  1895, 
The  Photomesomtitre.     Z'  Eclairage  Electrique. 

3.  Electrical  World,  xxvii:J509.  1896. 

1 


2 

out  in  a  masterly  manner  by  Blondel,  requires  a  somewhat 
elaborate  preliminary  calibration.  It  is  the  writer's  purpose  to 
describe  here  an  equipment  which  he  has  designed  for  the 
Photometric  Laboratory  of  Purdue  University,  where  it  is  now 
in  satisfactory  operation.  This  piece  of  apparatus,  while  embody- 
ing certain  features  of  Blondei's  apparatus,  combines  sim- 
plicity of  operation  with  adaptability  to  either  the  open  or  en- 
closed arcs. 

THEORY  OF  THE  METHOD. 

The  mean  spherical  intensity  and  the  mean  hemispherical  in- 
tensity of  a  source  whose  photometric  surface  is  one  of  a  revolu- 
tion are  given  by  the  expressions  : 


7ni  =  I  Ie  sin  6  d  6* 


10  sin  o  a  0. 

Where  1^  is  the  intensity  at  an  inclination  of  6  to  the  vertical' 
If  the  intensity  I0  be  taken  at  n  equal  intervals  through  180°, 
or  n'  equal  intervals  through  90°  in  a  vertical  plane,  we  may 
write 

^  n   ^—o 
as  the  mean  spherical  intensity  and 


as  the  mean  hemispherical  intensity — expressions  which  are  quite 
correct  if  n  and  n'  be  sufficiently  large. 

For  example,  let  us  consider  the  hypothetical  distribution  of 
intensity  shown  in  Fig.  1,  namely,  a  circle  tangent  to  a  vertica 
line.  Here  7  is  a  known  function  of  6  and  we  have 


=* 

t/  0 


'7T 

0 

=  78.5 
if  JQ  be  taken  as  100. 


Appendix. 


3 

Taking  now  A  0  =  15*  or  n  =  12,  we  have 

TABLE  I. 


100  sin8  0 


0 

15 

30 

45 

60 

75 

90 

105 

120 

135 

160 

175 


600. 


FIG.  1. 


Whence 


100  sin2  0   =  600  and  J      = 


2  X  12 


X  600  =  78.5 


It  thus  appears  that  with  n  —  12, 'the  approximate  formula 
yields  a  result  amply  correct. 

To  produce  on  the  photometer  screen  an  illumination  pro- 
portional to  the  mean  spherical  intensity  of  ,the  source,  it  is 
necessary,  as  the  formula  shows,  (1)  to  direct  towards  the 
photometer  the  beams  of  light  which  the  eye  of  an  observer 
would  receive  if  he  were  to  view  the  source  at  angular  intervals 
of  15  degrees  in  a  vertical  plane,  and  (*2)  to  reduce  the  intensity 
of  the  light  in  these  directions  in  the  ratio  of  the  sine  of  the 
angle  between  the  direction  of  view  and  the  vertical.  The 
method  of  accomplishing  this  is  described  below. 


FIG.  2. — Plan  and  Elevation  of  Photometer  Room. 


DESCRIPTION  OF  METHOD. 

A  ring  of  24  large  trapezoidal  mirrors,  M,  M,  surrounds  the 
arc.  This  system  of  mirrors  constitutes  a  truncated,  24-sided 
pyramid.  The  inclination  of  the  mirrors  to  the  axis  A  of  the 
system  is  such  that  the  eye,  placed  at  the  photometer  p,  sees  24 
images  of  the  lamp  L,  of  which  i/  is  the  horizontal  one,  precisely 
as  if  the  mirrors  being  absent,  one  were  to  travel  in  a  circle 
about  the  arc  in  the  plane  00'  stopping  at  15°  intervals.  Figs. 
3  and  4  show  the  aspect  of  this  series  of  images  from  a  point 


FIG.  3. — Arrangement  for  the  Determination  of  the  Mean  Spherical  Intensity. 
[The  slight  amount  of  dispiacement  in  Figs.  3  and  4  is  due  to  the  fact 
that  the  camera  could  not  be  placed  in  the  optical  center  of  the  system.] 

near  the  photometer.  The  first  figure  shows  the  entire  set  of 
images  as  used  in  the  determination  of  the  mean  spherical  in- 
tensity, and  the  second  figure  the  lower  images  only  for  the 
determination  of  the  mean  hemispherical  intensity,  as  in  the  case 
of  lamps  with  shades.  As  actually  used,  the  top  and  bottom 
mirrors  were  left  out,  not  because  there  may  not  be  light  in  these 


directions,  but  because  these  intensities,  when  multiplied  by 
sine  0°,  do  not  contribute  to  the  mean  spherical  intensity. 
Direct  light  from  the  arc  is  intercepted  by  a  black  screen  s. 

This  system  of  mirrors  serves  then  to  direct  the  light  to  the 
photometer  screen  in  the  chosen  directions.  The  second  con- 
dition is  that  the  intensity  of  each  beam  of  light  shall  be  reduced 
in  the  ratio  of  the  sine  of  the  vertical  angle.  I  have  done  this 
by  a  polygonal  glass  disk  D,  composed  of  as  many  sectors  as 
there  are  mirrors.  These  sectors  are  smoked  until  they  give  the 
desired  absorption.  In  order  that  the  film  of  smoke  may  be 
permanent,  the  ring  of  smoked  sectors  is  covered  by  two  plates 


FIG.  4. — Arrangement  for  the  Determination  of  the   Mean   Hemispherical   In- 
tensity. 

of  plane  glass.  These  plates  cover  but  do  not  touch  the  smoked 
surfaces.  The  three  thicknesses  of  glass  are  firmly  bound  to- 
gether, and  the  screen  as  a  whole  may  be  handled  without  fear 
of  changing  its  absorption.  The  precaution  must  be  taken  to 
thoroughly  clean  its  external  surfaces  before  making  measure- 
ments. An  essential  condition  to  the  success  of  this  method  is 
that  the  photometer  'screen  should  receive  light  through  any 
given  sector  from  the  image  in  the  corresponding  mirror  and 
from  no  other.  That  this  condition  is  fulfilled,  can  easily  be 
determined.  Thus,  if  all  the  mirrors  be  covered  except  the 
horizontal  one,  and  all  the  sectors  be  covered  except  the  sector 
just  above  the  horizontal,  that  is,  at  15°  A,  then  if  the  patch  of 
light  produced  by  this  arrangement  of  the  apparatus  fails  not 


upon  the  photometer  screen,  but  upon  the  black  surface  in  the 
vicinity  of  the  photometer,  the  required  condition  is  met.  The 
sectored  disk  is  best  put  in  place  by  replacing  the  photometer 
screen  by  a  cardboard  pierced  by  a  small  opening.  The  observer 
can  then  sight  through  this  hole,  and  ascertain  the  adjustment  of 
the  disk  with  reference  to  the  system  of  mirrors. 

CONSTANTS  OF  MIKRORS  AND  GLASS. 

The  mirrors  are  of  good  quality,  French  plate  glass.  Their 
reflection  coefficients  were  carefully  determined  for  the  in- 
cidence at  which  they  are  used.  Some  inequalities  were  found, 
as  would  be  expected,  although  the  maximum  difference  from 
the  mean  value  of  .815  is  only  ±  2.9  per  cent.  The  following 
table  gives  the  coefficients  of  the  24  mirrors. 

TABLE  II. 
Value  of  Mirror  Coefficients  KQ 


Mirror  Number. 

KB 

Mirror  Number. 

Se 

t 

.796 

»3 

.820 

•2 

.830 

»4 

.832 

3 

.803 

15 

.798 

4 

.814 

16 

.818 

5 

.791 

*7 

.818 

6 

.812 

18 

.809 

7 

.812 

19 

.798 

8 

.803 

20 

.bia 

9 

.832 

21 

.812 

*0 

.809 

22 

.812 

II 

•839 

23 

.830 

12 

•834 

24 

.812 

It  will  be  seen  that  these  coefficients  occur  in  pairs.  This 
would  lead  one  to  believe  that  two  mirrors  were  cut  from  one 
piece  of  glass.  An  inspection  of  the  edges  of  the  mirrors  showed 
that  this  was  very  probably  the  case.  -  The  values  are  so  nearly 
equal  that  for  purposes  of  arc-light  photometry  sufficient  accur- 
acy would  be  obtained  by  using  the  mean  value  of  .815.  How- 
ever, in  order  that  the  apparatus  might  be  used  for  the  measure- 
ment of  steady  sources,  I  have  made  up  for  variations  in  KQ  in 
the  smoking  of  the  corresponding  glass  sectors.  That  is  to  say, 
if  the  coefficient  of  a  particular  mirror  were  high,  the  corres- 
ponding glass  sector  was  smoked  a  little  heavier  than  would 
otherwise  be  done.  In  all  cases  the  formula 


=  (KQ  Kg)  sin  6  was  satisfied. 


s 


Where  K^  =  transmission  coefficient  of  glass 

ITa  —  transmission  coefficient  of  layer  of  smoke  corres- 

ponding to  angle  0. 

Ke  —  reflection  coefficient  of  mirror  at  angle  6 
KQ  =  reflection  coefficient  of  horizontal  mirror. 
Since  l£g  and  K*  must,  of  necessity,  be  obtained  together,  we 

have  as  the  required  transmission  coefficient  for  the  6  sector 

K  ^  sin  ^ 


This  value  was  computed  for  each  sector  and  the  glass  smoked 
accordingly.  It  will  be  seen  from  this  that  the  intensities  are 
cut  down  as  a  whole  in  the  ratio  K^  Ks\],  and  furthermore, 
separately  in  the  ratio  sin  6  :  1. 

The  mirrors  were  paired  and  put  in  position  according  to  the 
following  table  : 

TABLE  III. 

Position  of  Mirrors. 


Position. 

Mirrors. 

Mean  Constant  at  40° 

0 

6  and    7 

.812 

i5A 

22               24 

.812 

30  A 

9           M 

.832 

45A 

15           19 

.798 

6oA 

It               12 

•837 

-75A 

i             5 

•793 

I5B 

20                21 

.813 

3°B 

16           17 

.818 

2                2^ 

.830 

6oB 

10           18 

.809 

758 

3            8 

.803 

Constant  of  Mirror  behinc 

i  Photometer  at  12%*  =  .901. 

Some  care  and  skill  are  necessary  to  produce  a  uniform  coat- 
ing of  smoke  of  just  the  required  density.  I  have  found  it  con- 
venient to  use  a  sheet  iron  chamber,  fitted  with  a  suitable  flue, 
and  pierced  near  the  top  with  a  small  opening  for  the  introduc- 
tion of  the  glass.  This  chamber  must  be  placed  near  one  end  of 
the  photometer  bar  in  order  that  the  absorption  of  the  glass  may 
be  tested  as  frequently  as  may  be  necessary.  The  setting  of  the 
photometer  being  predetermined,  each  sector  is  smoked  until  it 
shows  the  required  absorption.  There  is  a  tendency  for  the  coat- 
ing to  form  most  heavily  near  the  edges  of  the  glass.  This  may 


9 

be  overcome  by  providing  a  guard  ring  of  glass  of  the  same 
thickness  as  the  piece  to  be  smoked,  the  whole  being  mounted  in 
a  convenient  holder.  The  best  results  will  be  obtained  by  hold- 
ing the  piece  of  glass  vertically  in  the  smoke  chamber,  occa- 
sionally reversing  the  piece.  Turpentine  is  a  good  combustible, 
but  it  must  be  introduced  into  the  receptacle  at  the  base  of  the 
chamber  in  small  quantities,  otherwise  the  combustion  will  be  so 
violent  as  to  produce  a  flocculent  'deposit  on  the  glass. 

In  testing  the  glasses  it  is  best  to  use  a  small  source  of  light, 
such  as  a  narrow  slit  in  front  of  a  straight  filament  glow-lamp. 
Any  inequalities  in  the  coating  of  smoke  can  be  detected  by  mov- 
ing the  glass  about  in  front  of  this  opening,  care  being  taken 
that  the  same  plane  is  maintained.  It  will  be  seen  in  Fig.  2 
that  the  incidence  of  the  light  upon  the  glass  is  not  quite  nor- 
mal. Care  was  taken  to  maintain  this  same  incidence  in  the  ab- 
sorption tests. 

At  J/8  is  shown  a  mirror  for  directing  the  light  from  the 
temporary  standard  to  the  photometer.  This  mirror  might  have 
been  omitted  had  not  the  limits  of  the  photometer  room  already 
been  taxed  to  the  utmost.  Still  better,  if  the  mirrors  were  from 
one  large  piece  of  glass,  the  direction  of  the  photometer  bar 
might  be  such  that  the  same  incidence  would  be  had  on  M%  as 
upon  the  others.  In  this  case,  the  correction  for  the  mirror  ab- 
sorption would  be  eliminated. 

The  illumination  upon  the  arc  side  of  the  photometer  screen 
is,  of  course,  very  intense.  It  is  necessary  to  reduce  this  illumin- 
ation. For  this  purpose,  I  have  used  a  rotating  wheel  w,  pro. 
vided  with  a  large  number  of  narrow  radial  slots.  It  is  quite  es- 
sential that  the  number  of  open  slots  should  be  large,  as  other- 
wise the  illumination  on  the  photometer  screen  will  be  seen  to 
beat  or  pulsate  when  measurements  are  being  made  on  the  alter- 
nating arc.  In  order  to  avoid  the  error  found  by  Ferry1  I  have 
determined  the  constant  of  this  wheel  by  direct  experiment  on 
the  arc  itself,  and  not  by  calculation.  The  mean  of  several  de- 
terminations gives 

Transmission  constant  sectored  wheel  =  Kv  =  .090 

The  number  of  slots  in  this  wheel  is  48,  which  gives  a  fre- 
quency amply  great  at  the  normal  speed  of  the  motor  used  for 
driving  the  wheel. 

1.  Physical  Review,  vol.  i,  p.  338. 


to 

A  possible  source  of  error  is  the  diffusion  of  the  smoked  glass 
disk.  That  is  to  say,  since  the  disk  receives  a  certain  flux  of 
light  dependent  upon  the  solid  angle  which  it  subtends  from 
each  image  as  a  center  and  upon  the  intensity  of  euch  image,  it 
becomes,  to  some  extent,  a  secondary  source.  The  direct  meas- 
urement of  this  is  a  matter  of  some  difficulty.  To  determine  if 
the  correction  for  this  diffusion  were  of  importance,  I  proceeded 
as  follows  :  The  longitudinal  screen  ss'  was  removed,  the  mirrors 
to  the  left  of  the  vertical  were  covered,  and  likewise  the  right 
half  of  the  sectored  glass  disk.  With  an  arc  of  ordinary  inten- 
sity in  the  center  of  the  mirror  system,  it  is  evident  that  the 
left  half  of  the  sectored  disk  receives  a  flux  of  light  about  equal 
to  that  which  it  would  normally  receive  with  the  longitudinal 
screen  in  position  and  the  mirrors  entirely  uncovered.  At  the 
same  time,  no  direct  light  from  the  images  falls  upon  the  pho- 
tometer screen.  Any  illumination  perceived  under  such  cir- 
cumstances would  be  due  to  the  diffusive  action  of  the  glass. 
As  a  matter  of  fact,  I  found  that  with  the  temporary  standard 
stopped  down  by  a  narrow  slit,  I  could  get  a  setting  in  this  way 
when  the  sectored  wheel  was  not  in  position,  but  when  this 
wheel  was  running  in  its  proper  place  the  correction  was  entirely 
negligible.  Hence  no  further  attempt  was  made  to  take  account 
of  it. 

The  distance  from  source  to  photometer  screen  is  large,  being 
nearly  nine  metres.  As  the  incidence  of  the  light  from  the 
temporary  standard  is  the  same  as  that  from  the  arc,  no  correc- 
tion is  here  necessary. 

A  working  equation  may  be  developed  as  follows  ;  Let 

d&    =  distance  from  arc  to  photometer  screen. 
ds     =  distance  from  temporary  standard  to  photometer  screen. 
KQ  =  reflection  constant  of  the  horizontal  mirror. 
KK  =  transmission  constant  of  clean  glasses. 
J5T8   =  reflection  constant  of  mirror  on  glow  lamp  side. 
KV  =  transmission  constant  of  wheel. 
n,  n'  =  number  of  mirrors. 

f     =  factor  due  to  the  lack  of  normal  incidence. 
The  illumination  due  to  the  arc  is 


*  = 


11 

and  that  due  to  the  standard  of  intensity  /8 


Equating  these  two  expressions,  we  have  for  the  mean  spher 
ical  intensity 


4  n  KQ  Kg  Kv  \dt 

Similarly  for  the  mean  hemispherical 


«•  K*          IdX  T 
±ri  K,  KgJTw  \dj 


With  the  following  numerical  values 

d&    =  865  cm.  n    =  12 

n'  =     7 

^0  =  -812  J£6=  .901 

/iTg  =  .690  JSTW=  .090 

These  equations  reduce  to 


which  are  the  working  equations  for  the  apparatus.  Values  of 
dB  are  recorded  on  a  drum  in  a  manner  already  described  by  the 
writer.1  (See  Fig.  2.) 

(d  V 
—M     are   obtained   by   laying  a  graduated  T- 


1.  Physical  Review,  vol.  vii,  p.  239,  1898. 


square  on  the  records  obtained  on  the  record- 
ing drum.  A  single  covering  on  the  drum 
suffices  for  the  record  of  many  tests.  The 
records  may  then  be  worked  out  at  the  leis- 
ure of  the  operator.  These  records  have 
always  the  same  general  characteristics, 
namely,  many  settings  close  together  with 
scattered  settings  at  each  end.  Figure  5  is 
a  specimen  record,  and  shows  the  usual 
range  of  fluctuation.  The  number  of  set- 
tings here  is  30.  This  large  number  is  nec- 
essary because  of  the  fluctuations  in  the  in. 
tensity  of  the  arc,  even  with  the  steadying 
effect  peculiar  to  the  multiple  mirror  method. 
With  hand  fed  arcs,  a  smaller  number  will 
suffice  to  give  a  value  representative  of  the 
average  performance  of  the  arc.  For  the 
distribution  curves,  it  suffices  to  uncover  the 
mirrors  in  pairs  and  make  settings  in  the 
usual  way.  The  appropriate  mirror  constants 
must,  of  course,  be  used  in  working  up  the 
results. 

As  a  check  on  the  accuracy  of  the  integrat- 
ing method  as  compared  with  the  usual  me- 
thod, I  give  the  results  of  a  test  on  an  arc 
of  the  enclosed  type.  The  value  obtained 
from  the  Rousseau  diagram  is  308.  That 
by  the  method  described  in  this  paper,  319. 
This  agreement  is  within  3.4  per  cent.  When 
one  considers  the  difficulty  in  maintaining 
an  automatic  feed  arc  under  constant  con- 
ditions during  the  time  required  to  take  the 
distribution  curve,  this  must  be  considered  as 
a  very  satisfactory  agreement. 

APPENDIX. 

The  product  of  the  intensity  /  and  the 
area  of  an  elementary  zone  of  radius  r  is 


=  2  TT  IP  L  sin  6  d  6. 


13 


The  mean  spherical  intensity  is 


r     —  *J 

-/ma 


The  graphic  method  due  to  Rousseau  is  shown  in  Fig.  6. 
O  a  ft  is  the  given  distribution.  Draw  a  semi-circle  of  conven- 
ient radius.  Project  on  the  vertical  c  d  the  points  A,  k.  At  ft 
g,  lay  off  the  corresponding  intensities  /15  /2.  The  area  c  m  np  d 


FIG.  6. 


may  be  taken  with  a  planimeter.     This  area  divided  by  the  base 
c  d  gives  the  mean  spherical  intensity,  for 


dd  = 


d  s 


d  s  sin  6  —  d  y 


PART  IV. 


THE  LIFE    AND    EFFICIENCY   OF    COMMERCIAL,   BRANDS 
OF  CARBONS  FOR  INCLOSED  ARCS. 


PART    IV. 

THE  LIFE  AND  EFFICIENCY  OF  COMMERCIAL  BRANDS    OF 
CARBONS   FOR   INCLOSED   ARCS. 

In  this  part  of  the  work  the  apparatus  described  in 
Part  III  has  been  used. 

PRELIMINARY   TEST 

In  order  to  ascertain  the  behavior  of  the  apparatus 
on  an  actual  life  test,  several  preliminary  runs  were 
made.  Two  of  the  most  characteristic  of  these  are 
selected  for  presentation  here.  A  no  volt,  constant- 
potential,  alternating-current  lamp,  with  shade  and 
opalescent  inner  globe  (being,  in  fact,  one  of  the  lamps 
used  in  the  subsequent  test),  was  tested,  at  intervals  of 
about  ten  hours  during  its  life.  The  results  obtained 
are  to  be  found  in  Table  I  and  Figure  7. 

The  first  point  was  discarded  because  of  uncertain 
conditions,  but  otherwise  the  curve  is  fairly  indicative 
of  the  behavior  of  such  a  lamp.  The  arc  appears  be- 
neath the  shade  between  the  fourth  and  fifth  tests. 
This  event  is  accompanied  by  a  rise  in  the  curve,  due 
to  the  strengthening  of  the  horizontal  intensity.  This 
effect  will  be  noticed  in  most  of  the  curves  to  follow. 


TABLE  I 


Test 

Time 

Intensity 

I 

2.6  Hours 

273  H.  U. 

2 

12.8 

249 

3 

22.1 

237 

4 

33-5 

236 

5 

45-5 

2m 

6 

56.1 

233 

7 

66.8 

233 

8 

76.9 

200 

t   0     M      HO      /«T 


FIG.  7. — LIFE  TKST,  SHOWING  MEAN  HEMISPHERICAL  INTENSITY  FOR  iio-VoLT, 
CONSTANT-POTENTIAL,  ALTERNATING-CURRENT  LAMP  WITH  SHADE. 


Then  comes  a  dip  followed  by  a  second  maximum. 
The  arc  is  now  about  midway  between  the  bottom  of 
the  shade  and  the  base  of  the  globe.  This  appears 
to  be  a  very  effective  position.  But,  after  this,  the 
arc  is  descending  into  a  region  of  the  globe  more  or 
less  heavily  coated  with  ash  and  carbon  dust,  and  the 
decline  in  intensity  up  to  the  point  of  extinction  is 
rapid. 

In  a  life  history  like  this  we  have  probably  many 
minor  influences  that  cannot  be  taken  into  considera- 
tion, but  undoubtedly  the  prime  causes  for  the 
observed  changes  in  intensity  are  (i)  the  descending 
arc,  and  (2)  the  formation  of  a  globe  coating.  These 
influences  are,  much  of  the  time,  opposing  ones.  The 
resultant  effect,  as  shown  in  the  later  curves  of  this 
report,  will  be  modified  according  to  the  predomi- 
nance of  one  or  the  other  influence. 

An  inspection  of  the  inner  globes  shows  that  the 
coating  forms  most  heavily  in  two  regions.  Near  the 
top  of  the  globe  is  a  zone  of  cream-colored  ash,  quite 
free  from  carbon  dust.  This  zone  follows  the  arc  in 
its  downward  course,  but  always  with  a  diminishing 
thickness  of  the  deposit.  While  there  may  be  a  con- 
siderable loss  of  light  because  of  this  formation,  the 
increasing  available  light  flux  due  to  the  descending 
arc  may  oftentimes  overcome  it,  especially  in  the 
case  of  alternating  lamps  with  wide,  dark  surfaces 
above  the  globe.  (See  the  preceding  report.)  Near 
the  bottom  of  the  globe  is  a  zone  of  ash  lighter  in 
color  than  that  at  the  top.  Mixed  with  this  ash  is  a 
considerable  amount  of  carbon  dust.  The  amount  of 
this  dust  is  dependent  upon  the  steadiness  of  opera- 
tion of  the  lamp.  If  the  lamp  feeds  frequently, 
or  if  the  carbons  chatter,  this  deposit  will  be  found 
heavier  than  usual. 


10 


TABLE  II 


Test 

Time 

Intensity 

I 

5.2  Hours 

140  H.  U. 

2 

16.3 

130 

3 

23-3 

120 

4 

33-6 

118 

5 

44-9 

123 

6 

55.~ 

123 

7 

66.6 

125 

8 

76.8 

107 

9 

87.1 

114 

FIG.    8. — LIFE    TEST,    SHOWING    MEAN    SPHERICAL    INTENSITY    OF    IIO-VOLT, 

CONSTANT-POTENTIAL,  ALTERNATING-CURRENT   LAMP 

WITH  DIFFUSING  SHADE. 

In  Table  II  and  Figure  8  are  to  be  found  the 
results  of  a  second  preliminary  run.  This  lamp  was 
of  the  same  type  as  that  just  mentioned,  except  that 
the  shade  was  replaced  by  an  opal  spherical  globe. 
The  ordinates  of  the  curve  are  here  the  mean  spheri- 
cal intensity.  As  would  be  expected,  this  type  shows 
but  little  change.  The  globe  itself  is  the  chief  source 
of  light,  and  the  position  of  the  arc  in  it  has  only  a 
secondary  effect.  The  downward  trend  of  this  curve 
must  be  due  to  the  coating. 


LIFE     AND     EFFICIENCY    OF    COMMERCIAL    BRANDS    OF 

CARBONS 

The  preliminary  measurements  just  described  indi- 
cated that  the  photometric  apparatus  would  adequately 
answer  the  purpose  for  which  it  was  designed. 
Preparations  were  therefore  made  to  test  samples  of 
five  brands  of  carbons  for  inclosed-arc  lighting,  these 
brands  being  well  known  and  obtainable  in  the  open 
markets  of  to-day.  The  samples  represent  the  prod- 
uct of  three  American  and  two  European  manu- 
facturers. 

The  carbons  were  burned  in  six  no-volt, 
alternating-current  lamps,  provided  with  opalescent 
inner  globes  and  shades.  (See  Figure  4.)  Of  these 
lamps,  five  were  fitted  with  the  particular  brand  of 
carbons  to  be  tested,  the  sixth  lamp  being  held  in 
reserve,  lest  accident  or  poor  operation  should  require 
a  substitution.  Experience  showed,  in  one  or  two 
cases,  the  wisdom  of  this  precaution.  The  lamps 
were  suspended  from  the  radial  arms  of  the  wheel 
shown  in  the  foregoing  plan  of  the  apparatus.  In  this 
position,  the  lamps  ran  out  the  life  of  one  trimming. 
With  few  exceptions,  the  only  stops  were  at  the 
close  of  the  laboratory  day.  Counting  all  interrup- 
tions, the  average  run  was  about  eight  hours.  Not 
infrequently,  a  steady  run  of  twelve  hours  occurred. 
These  conditions  are  probably  somewhat  better,  and 
certainly  no  worse,  than  the  average  conditions  of 
practice.  The  carbon  life  shown  in  the  following 
results  seems  to  corroborate  this  statement,  as  the 
life  usually  claimed  for  lamps  of  this  type  is  eighty 
to  one  hundred  hours.  It  may  be  well  to  note  just 
here  that  the  duration  of  burning  in  these  lamps  is 
limited  by  the  allowable  range  of  descent  of  the 
upper  carbon  h®lder.  This  range  is  a  fixed  quantity. 


i8 


The  life  on  one    trimming  may  therefore  be  expressed 
by  the  simple  formula, 


,= 


where  lo  is  the  fixed  range  referred  to  and  ru,  rt  the 
respective  rates  of  burning  of  the  upper  and  lower 
carbons.  The  life,  clearly,  will  be  a  maximum  for 
that  case  in  which  the  sum  of  these  rates  is  a 
minimum. 

A  lamp  fitted  with  a  shade  is  in  itself  an  intima- 
tion that  only  the  downward  flux  of  light  is  of  value. 
The  logical  basis  of  comparison  in  such  cases  is  the 
mean  hemispherical  intensity,  or,  if  desired,  the  down- 
ward flux  of  light,  which  is  2**  x  the  mean  hemi- 
spherical intensity.  In  the  following  carbon  tests,  the 
mean  hemispherical  intensity  is  the  quantity  deter- 
mined. In  the  curves  it  will  be  found  plotted  as  an 
ordinate  against  time  as  an  abscissa. 

In  what  follows,  the  brands  of  carbons  will  be 
designated  by  Roman  numerals,  I,  II,  etc.,  in  the 
order  of  the  tests,  while  the  lamps  will  be  referred  to 
as  A,  B,  etc.  The  upper  carbon  in  all  the  tests  was 
cored,  the  lower  carbon  solid. 

Carbons  I.  The  results  of  the  first  test  are  to  be 
found  in  tables  III  and  IV.  Figure  9  shows  the  life 
curves  of  the  individual  lamps  in  thin  lines  and  the 
mean  performance  of  the  five  lamps  in  the  thick  line. 
We  note  here  that  the  trend  of  the  mean  curve  is, 
in  the  main,  upward.  After  eighty-five  hours'  burning, 
the  lamps  show  ten  per  cent  better  performance  than 
at  the  start.  The  mean  curve  has  the  same  general 
shape  as  the  preliminary  curve  (Figure  7).  Lamp  B 
distanced  its  companions  by  showing  a  life  of  114 
hours.  On  the  third,  fourth,  seventh  and  eighth  tests 


I9 


the  points  are  quite  close  together  ;  on  the  other  tests 
there  is  more  or  less  divergence.  Why  this  difference? 
The  use  of  an  apparatus  for  recording  the  changes  in 
the  arc  length  in  lamps  such  as  these  has  convinced 


TABLE  III 

CARBONS    I 
LAMP  A 


Test 

Time 

Intensity 

1 

3.2  Hours 

202    H.   U. 

2 

13-7 

222         " 

3 

23.1 

193         " 

4 

33-2 

I96         " 

5 

46.8 

202 

6 

54-3 

173 

7 

63-9 

2O2 

8 

74-0 

214 

9 

84.6      " 

20O 

10 

92.6      " 

189 

LAMP  B 


I 

3.3  Hours 

194  H.  U. 

2 

13.7   " 

170 

3 

23.2 

179 

4 

33-0   " 

194 

5 

44.2 

205 

6 

54-2 

198 

7 

63.7   " 

212     ' 

8 

73-8   " 

222     ' 

9 

844 

231 

10 

95-7 

184 

ii 

III.O 

I87     ' 

12 

II4-3 

152 

LAMP  C 


I 

3.4  Hours 

217  H.  U. 

2 

14.0   " 

204   " 

3 

23.2 

187   " 

4 

33-0 

188 

5 

44  -2 

213   " 

6 

54-1   " 

229 

7 

63.5   " 

203 

8 

73-6   " 

221    " 

9 

84.2 

207    " 

10 

94.2   " 

162 

2O 


TABLE   III — Continued. 
LAMP  D 


I 

3.3  Hours 

223  H.  U. 

2 

14.0 

217 

3 

23-5 

190 

4 

33-2 

194 

5 

44-5 

231 

6 

54-4 

207 

7 

63.8 

211 

8 

73-8 

213 

9 

844 

251 

10 

95-8 

188 

LAMP  E 


I 

3.6  Hours 

176  H.  U. 

2 

14.2 

186 

3 

23.8 

173 

4 

33-3 

187 

5 

44-6 

200 

6 

54-5 

228 

7 

63.8 

2OI 

8 

73-9 

220 

9 

84-5 

216 

10 

95-9 

177 

ii 

97.1 

I67 

me  that  these  differences  are  due  in  a  large  measure 
to  changes  in  the  arc  length.  Now,  the  time  between 
successive  feedings  is,  in  a  well  regulated  lamp,  an 
interval  considerably  longer  than  that  required  for  a 
test.  During  this  interval  between  feedings,  the  arc 
tends  to  grow  steadily  longer.  It  has  been  shown  by 
Blondel  and  by  Ayrton  that  the  luminous  intensity 
of  an  arc  at  constant  current  is  dependent,  in  a  very 
important  way,  on  the  arc  length.  It  seems  clear, 
then,  that  tests  such  as  those  described  here  might  at 
one  time  find  the  arcs  of  approximately  the  same 
length,  and  at  another  time  differing  considerably  in 
length.  Lack  of  homogeneity  in  either  upper  or  lower 
carbon  might  also  have  an  effect.  It  is  evident  that 
any  constant  difference  in  the  carbons  or  in  the  trans- 
parency of  the  inner  globes  would  be  made  manifest 
by  a  permanent  separation  of  the  life  curves. 


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Inner  globe,  initial  weight,  grammes  
Inner  globe,  final  weight,  grammes  
Inner  globe,  gain  weight,  grammes  

CARBONS 

S  :  :  :  jj      :  : 

'             I       I   '  o  12   I   !       : 

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h/5^i-i>H*4~'1J1JlL>G 
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22 


While  the  length  of  these  curves  indicates  the  'ife 
of  the  carbons  and  the  mean  ordinate  their  light 
value,  these  quantities  alone  are  not  a  sufficient  measure 
of  the  worth  of  the  carbon.  The  area  between  the 
curves  and  the  X-axis  is  an  important  basis  of  comparison. 
This  area  has  been  found  for  each  test.  It  is  measured 
in  Hefner-unit-hours.  For  Carbons  I  this  quantity  is 
20,200  or  202  hecto-Hefner-kours.  The  mean  intensity 
is  202  Hefner  units,  and  the  life  on  one  trimming  100 


FIG.  9. — INTENSITY  LIFE  TESTS  OF  CARBONS  I. 

hours.  To  eliminate  the  lamp  from  the  problem,  the 
table  shows  the  Hefner-unit-hours  per  unit  length  of 
carbon  consumed  and  also  per  unit  mass  consumed,"'" 
which  last  leaves  the  dimensions  of  the  carbon  out  of 
the  question.  These  matters  will  be  more  fully 
discussed  in  the  final  summing  up  of  the  tests. 

Carbons  II.  The  records  for  this  set  of  carbons 
are  to  be  found  in  Tables  V  and  VI  and  in  Figure 
10.  The  mean  life  is  practically  ninety-nine  hours. 

*To  facilitate  comparison  with  other  results,  I  have  used  both 
centimeter  and  inch  units. 


23 

However,  Lamp  A  showed  the  brief  life  of  62.5 
hours.  There  must  have  been  some  imperfection  in 
the  fit  of  the  gas  cap,  although  every  precaution  was 
taken  to  secure  impartial  treatment  in  this  as  in  every 
other  respect.  If  it  is  justifiable  to  exclude  A,  we  find 


TABLE  V 

CARBONS    II 
LAMP  A 


Te=t 

Time 

Intensity 

I 

i.o  Hours 

157  H.  U. 

2 

u.  8       " 

238       " 

3 

21.7       ' 

228 

4 

32.0 

209         ' 

5 

42.2       " 

209 

6 

523       " 

221 

7 

62.5 

219 

LAMP  B 


I 

i.i  Hours 

240  H.  U. 

2 

8.3 

203   " 

3 

17  9 

1 

218 

' 

4 

28.2 

1 

220 

• 

5 

38.3 

' 

219 

' 

6 

49  4 

' 

215 

' 

7 

60.0 

1 

232 

• 

8 

69.8 

i 

233 

1 

9 

81.8 

1 

241 

4 

10 

91.7 

' 

243 

' 

ii 

103.2 

193 

LAMP  D 


I 

i  i  Hours 

187  H.  U. 

2 

12.0    " 

192   " 

3 

21.6    " 

188   " 

4 

31-9 

203 

5 

42  o 

203   '* 

6 

52.0 

216   " 

7 

62.5  ' 

203   " 

8 

72.3 

230 

9 

84.2 

205 

10   * 

94.1 

203   " 

ii 

108.4 

181   " 

24 

TABLE    V— Continued. 
LAMP  E 


I 

2.2  Hours 

217  H.  U. 

2 

12.8   " 

224   " 

3 

23-9   " 

220 

4 

343 

2I4    " 

I 

45.7   ll 
56.7   " 

227 
233 

7 

66.4   " 

252 

8 

76.4   " 

213 

9 

86.8   " 

174 

10 

979   " 

158    " 

LAMP  F 


1 

1.3  Hours 

213  H.  U. 

2 

12.2 

239   " 

3 

22.  0    " 

258   " 

4 

32.5    " 

244 

5 

42.6    " 

258  M 

6 

52.7 

239 

7 

63.2 

263  " 

8 

73-0   " 

230   "' 

9 

85.0   " 

241  " 

10 

949 

218 

ii 

109.1 

209   " 

FIG.  10. — INTENSITY  LIFE  TESTS  OF  CARBONS  II. 


.? 

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26 


a  life  of  107.9  hours.  The  Hefner-unit-hours  rise  in 
such  case  to  23,800.  The  performance  of  A  indicates 
that  the  life  of  an  inclosed  arc  may  be  seriously 
curtailed  by  causes  not  easily  detected. 

The  mean  curve  in  this  test  rises  to  a  maximum 
at  sixty  hours'  life.  Lamp  F  shows  a  somewhat 
remarkable  performance  both  as  regards  intensity  and 
life.  A  mean  intensity  of  238  Hefner  units  is  maintained 
throughout  in  hours,  or  a  yield  of  264  hecto-Hefner- 
hours,  which  is  about  double  the  yield  of  A. 

Carbons  III.  The  records  for  this  set  of  carbons 
are  to  be  found  in  Tables  VII  and  VIII  and  in 
Figure  n.  As  regards  life,  these  carbons  show  a 

TABLE  VII 

CARBONS    III 
LAMP  A 


Test 

Time 

Intensity 

I 

3.4  Hours 

211    H.   U. 

2 

21.9 

22O 

3 

34-0 

223 

4 

44.2 

2I9 

5 

54-r 

218 

6 

63.7 

208 

7 

736 

I84 

8 

84.0 

I98 

9  * 

98.6 

199 

10 

108.6 

224 

ii 

118.2 

183 

LAMP  B 


I 

3.5  Hours 

259  H.  U. 

2 

21.9 

239 

3 

34-0 

224 

4 

44.2 

239 

5 

54-1 

231 

6 

63.6 

229 

7 

•  73-5 

205 

8 

83-9 

219 

9 

98.5 

195 

TABLE  Mil— Continued. 
LAMP  D 


I 

3.6  Hours 

207  H.  U. 

2 

22.7 

219 

3 

34-6 

227 

4 

44.8 

233 

5 

54-7 

228   * 

6 

63.2 

232   ' 

7 

73-1 

234 

8 

83.5 

202 

9 

98.3 

217   ' 

10 

108.2 

245   " 

ii 

118.3 

183   " 

12 

128.6 

230   " 

LAMP  E 


I 

3.6  Hours 

234  H.  U. 

2 

22.9 

248   " 

3 

34-8 

238 

1 

4 

45  o 

241 

i 

5 

55-0 

236 

4 

6 

64-5 

233 

1 

7 

74-1 

192 

* 

8 

84.5 

221    " 

9J 

99.1 

' 

203    " 

10 

109.0 

t 

223    " 

ii 

114.0 

199 

LAMP  F 


I 

3.7  Hours 

235  H.  U. 

2 

22.2 

253 

i 

3 

34-2 

250 

i 

4 

44  5 

250 

' 

5 

543 

235 

' 

6 

63.8 

238 

4 

7 

736 

221 

t 

84.0 

221 

« 

9 

98.7 

211 

* 

10 

108.5 

216 

' 

ii 

117.7 

149 

noteworthy  performance.  The  mean  life  is  115.6 
hours,  and  the  maximum  life  129  hours.  The  mean 
curve  does  not  show  the  tendency  to  rise  shown  in 
the  case  of  Carbons  1,  although  as  a  whole  it  lies 
high.  By  weight,  the  per  cent  ash  and  dust  is  about 
the  same.  An  inspection  of  the  inner  globes  after 
the  tests  showed  that  the  deposit  near  the  base  of 


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29 


the  globe  in  Case  III  was  darker — that  is,  contained 
more  carbon  dust  than  in  Case  I.  This  is,  in  my 
opinion,  the  cause  of  the  drooping  tendency  to  be 
seen  in  the  mean  curve  of  Carbons  III  after  forty- 
five  hours.  In  this  connection,  it  is  important  to  note 
that  the  number  of  extinctions  in  these  tests  was 


* 


FIG.  ii. — INTENSITY-LIFE  TESJS  OF  CARBONS  III 

somewhat  greater  than  in  the  case  of  Carbons  I  and 
II.  The  carbon  dust  is  due,  in  large  part,'  to  the 
pounding  or  chattering  of  the  carbons  at  the  start. 

These  carbons  show  a  mean  performance  of  252 
hecto-Hefner-hours. 

Carbons  IV.  The  records  for  this  brand  of  car- 
bons can  be  found  in  Tables  IX  and  X,  while  the 
life  curves  are  to  be  seen  in  Figure  12.  The  mean 
life  curve  is  an  exceptionally  good  one  and  shows  in 
a  very  satisfactory  manner  the  changes  that  occur  in 
the  luminous  intensity  of  a  lamp  of  this  type  during 
its  carbon  life. 

These  carbons  show  a  superior  luminous  intensity 
coupled  with  long  life.  A  mean  intensity  of  259 


30 

TABLE  IX 

CARBONS     IV 
LAMP  A 


Test 

Time 

Intensity 

I 

4.42  Hours 

239  H.  U. 

2 

14.9 

259       " 

3 

25.4 

241 

4 

35-6 

228       " 

5 

49.0 

250       " 

6 

62  8 

.   274 

7 

79.8 

253 

8 

91.9 

242 

9 

102.3 

238       " 

10 

II7-5 

271       " 

LAMP  B 


Test 

Time 

Intensity 

I 

4.5    Hours 

254  H. 

U. 

2 

15  0 

264 

3 

25-5 

264 

4 

35-7 

236 

5 

49.0 

272 

6 

63-1 

268 

7 

79-9 

278 

8 

91.9 

253 

" 

•9 

102.3 

260 

" 

10 

108.8 

225 

" 

CARBONS  IV 
LAMP  B 


Test 

Time 

Intensity 

I 

4.6    Hours 

303  H.  U. 

2 

15-0 

340 

3 

25  5 

278      " 

4 

35-5 

272       " 

5 

49.1 

301 

6 

62.9 

278      " 

7 

80.0 

349 

8 

85.6 

231 

31 


TABLE  IX—  Continued 
LAMP  E 


Test 

Time 

Intensity 

I 

4.7    Hours 

224  H    U. 

2 

15.1     " 

262      "    • 

3 

25.5 

241      V 

4 

35-8 

263      " 

5 

48.4 

264      " 

6 

63.2 

269      " 

7 

80  i 

277 

8 

92.1 

260 

9 

102.4 

244 

10 

109.5 

252 

LAMP  F 


Test 


Time 


Intensity 


I 

4.8  Hours 

249  H  U.. 

2 

15-2 

271   " 

3 

25.6    " 

259 

4 

35-7    " 

285   " 

5 

49  2 

275 

6 

63.1 

274 

7 

80.0 

249 

8 

93-0 

223   " 

9 

102  3 

276   " 

10 

in.  6    " 

207   " 

FIG.  12. — INTENSITY-LIFE  TESTS  OF  CARBONS  IV 


X 

IV 


LE 


TAB 

CARB 


2 

K 

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Inner  globe,  initial  weight,  grammes  
Inner  globe,  final  weight,  grammes  
Inner  globe,  gain  weight,  grammes  

CARBONS 

iii 

Current,  mean.  .  .•  
Power  in  lamp  
Mean  watts  per  H.  U  
Power  factor  of  lamp  
Life  of  one  trimming,  hours  

1  if^  r>pr  inrh  rarhon  honrc 

Life  per  centimeter  carbon,  hours  
Life  per  gramme  carbon,  hours  
Luminous  intensity,  H.  U  
H.  U.  hours  of  lamp  
H.  U.  hours  per  inch  
H.  U.  hours  per  centimeter  

'c  -5  o  'e  .£  O  'e  '5  'c  "c  O  °  °  °  a;  •-  •-  ^  —  3  >  "c 
M^feOH^foU^i-<i-HMHHHHUOHQQ'>JU2I<lK; 

33 


Hefner-units  is  maintained  throughout  a  life  of  some 
1 06  hours — a  yield  of  more  than  275  hecto-Hefner- 
hours.  At  the  same  time,  the  individual  lamp  curves 
lie  for  the  most  part  close  together,  indicating  a  uni- 
formity of  quality  .in  the  carbons. 

Carbons  V8  Tables  XI  and  XII  and  Figure  13 
exhibit  the  results  of  the  tests  on  this  brand  of  car- 
bons. The  luminous  intensity  is  seen  to  be  relatively 
low  and  the  life  short.  These  carbons  have  cores  of 
a  very  loose  structure.  When  the  upper  carbon  is  a 


FIG.  13. — INTENSITY-LIFE  CURVES  OF  CARBONS  V 


cored  one,  the  material 
distance    above    the    arc 


of  the  core  for  a  considerable 
falls  out  under  the  feeding 
action  of  the  lamp.  Meanwhile  an  excessively  long 
arc  of  low  luminosity  is  drawn.  The  result  was  cor- 
roborated by  taking  autographic  records  of  the  opera- 
tion of  the  lamps  on  an  apparatus  showing  the 
fluctuations  in  the  arc  length.  The  mean  life  of  these 
carbons  is  but  eighty-six  hours,  and  the  mean  in- 
tensity but  196  Hefner-units. 

In   Figure   14  the  mean    curves   for  the  five  brands 


34 


TABLE   XI 

CARBONS  V 

LAMP  A 


Test 

Time 

Intensity 

I 

3  I    Hours 

184  H.  U. 

2 

12.9 

160       " 

3 

24.4 

152       " 

4 

37-5 

165-5    4 

5 

52.1 

193 

6 

62.1 

182 

7 

72-9         " 

202       " 

8 

90  7 

179 

LAMP  B 


Test 

Time 

Intensity 

I 

3  I   Hours 

192  H.  U. 

2 

12.9 

159 

3 

24.6 

181       " 

4 

37-7 

164 

5 

52.3         " 

173 

6 

62.3         " 

196 

7 

73-2 

198       " 

8 

91  i 

179 

9 

IOI.O 

225 

LAMP  D 


Te^t 

Time 

Intensity 

I 

3.2    Hours 

208  H    U. 

2 

13.0 

203        " 

3 

24.7 

133 

4 

57-2 

204 

5 

52.4 

193 

6 

62.2 

223         " 

7 

73-0 

237 

8 

85.1 

227 

LAMP  E 


Test 

Time 

Intensity 

I 

3.2    Hours 

193   Hours 

2 

I3-I 

184        " 

3 

24.7 

163        " 

4 

37-8         " 

174 

5 

52.5 

205 

6 

62.5 

233 

7 

73-2 

227 

8 

87.9 

224 

35 


TABLE  XI— Continued 

CARBONS  V 

LAMP  F 


Test 

Time 

Intensity 

I 

3.3    Hours 

181  H.  U. 

2 

13.1 

172 

3 

24.8 

191 

4 

37-8 

195 

5 

52.6 

191 

6 

62.5 

193 

7 

73-5 

211 

8 

77-6 

209 

of  carbons  are  plotted  on  one  sheet.  The  superiority 
of  Brand  IV  in  intensity  is  here  made  manifest.  It 
is  interesting  to  note  that  all  of  the  four  remaining 
brands  came  to  about  the  same  intensity  after  seventy- 


4f  30    SS    40 


FIG.  14.  —  MEAN  CURVE  OF  THE  FIVE  BRANDS  OF  CARBONS 

five   hours  of    life,   although    the    divergence    prior    to 
this  time  is  quite  marked. 

These    brands    of    carbons    may    be    compared    in 
several    ways.      From    a    mere    standpoint    of    life,    the 


36 

order  of  merit  is  III,  II,  IV,  I,  V,  the  results  on 
Lamp  A  being  excluded  from  Carbons  II  (see  page 
23).  That  is  to  say,  an  American  brand  leads,  fol- 
lowed by  two  European  brands.  Including  Lamp  A 
in  Carbons  II,  the  order  is  III,  IV,  I,  II,  V,  the 
American  Brand  I  rising  to  third  place.  From  the 
standpoints  of  intensity  and  intensity  x  life,  the  order 
is  IV,  III,  II,  I,  V.  Here  the  European  Brand  IV 
has  a  distinct  lead.  The  American  Brand  III  lies  in 
second  place,  closely  followed  by  the  second  Euro- 
pean Brand  II. 

The  life  per  inch  of  carbon  in  these  tests  runs 
from  13.7  hours  in  the  case  of  Brand  V  to  18.4  in 
the  case  of  Brand  III.  The  order  of  merit  in  this 
respect  is  the  same  as  the  life  order  given  above. 

First  and  Second  Investigations — (Continued) 

Owing  to  the  growing  importance  of  series  arcs 
of  the  inclosed  type,  it  has  seemed  very  desirable  to 
make  a  sufficient  number  of  tests  of  both  the  direct- 
current  and  alternating-current  lamps  to  get  a 
measure  of  their  relative  worth.  In  Table  XIII  and  in 
Figure  15  are  embodied  the  results  of  a  distribution 
test  on  a  direct-current  series  lamp.  This  lamp  is 
provided  with  opalescent  inner  and  clear  outer  globes. 
The  power  consumption  is  476  watts.  With  seventy 
volts  at  the  terminals,  it  takes  6.8  amperes.  It 
yields  a  mean  spherical  intensity  of  266  Hefner  units 
and  a  mean  hemispherical  intensity  of  329  Hefner 
units.  The  curve  is  a  very  effective  one  for  street 
lighting,  as  the  intensity  is  strong  between  the  hori- 
zontal and  fifteen  degrees  below.  If  used  for  street 
lighting,  such  a  lamp  would  be  greatly  improved  by 
replacing  the  clear  outer  globe  with  a  suitable  shade. 


to 


to 


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•*;*.***: ; | •    •    •    •  c 

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sse£%EZe^£-»        :g     :  :  :    «^.l  :     g^ 

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l?||!M!|!tf|^i!lli 

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1)    <U    HJ 

c  c  c 

c  c  c 


The  efficiency  of  this  lamp  is  high,  being  1.78  watts 
per  mean  spherical  Hefner  unit,  and  1.41  watts  per 
mean  hemispherical  Hefner  unit. 

In  Table  XIV  and  Figure  16  are  embodied  the 
results  of  a  test  on  the  series  alternating-current  lamp, 
provided  with  an  opalescent  inner  globe  and  a  metallic 
shade.  A  small  reading  is  possible  at  fifteen  degrees 

TABLE    XIII 

D.  C.  SERIES 

LAMP   67 


Angle 

Intcns 

ity 

75°  A 

60°  A 

48  H. 

U. 

45°  A 

117 

30°  A 

246 

15°  A 

302 

Hor. 

348 

15°  B 

372 

30°  B 

37i 

45°  B 

364 

60°  B 

229 

75°  B 

150 

Globes 


E.  M.  F 

Current 

Watts 

Mean  hemispherical  Intensity,  H.  U. 

Mean  spherical  Intensity,  H.  U 

Watts  per  mean  spherical,  H.  U. 
Watts  per  mean  hemispherical,  H.  U 


Clear  Outer 
Opalescent  Inner 


70  volts 
6.8  amperes 
476. 

329. 
266. 

1.78 

1.41 


above,  but  above  this  point  no  light  is  perceptible. 
This  lamp  takes  397  watts  with  seventy  volts  impressed 
and  a  current  of  6.6  amperes.  It  shows  a  power 
factor  of  .86.  The  mean  hemispherical  intensity  is 
314;  that  is  to  say,  it  gives  nearly  the  same  light 
below  the  horizontal  as  does  the  direct-current  lamp 
provided  with  clear  outer  globe  and  no  shade.  The 


39 


efficiency  is   1.26  watts  per  mean  hemispherical  Hefner 
unit.      As    producers    of    light    below    the    horizontal, 


FIG.  15.— LAMP  67— DIRECT-CURRENT  SERIES  INCLOSED-ARC,  CLEAR  OUTER 
AND  OPALESCENT  INNER  GLOBES 

the    two    lamps    equipped    in    the    manner    stated    are 
about    equally    efficient,    but    the    direct-current    lamp 


FIG.  16. — LAMP  268 — ALTERNATING-CURRENT  SERIES   INCLOSED-ARC,   OPAL 
'  ESCENT  INNER  GLOBE  AND  METALLIC  REFLECTOR 

would,    of    course,    be    considerably    superior    if    fitted 
with  a  shade  instead  of  a  clear  outer  globe. 


I  wish   to  acknowledge    the  very 

efficient  services  of  my  assistant,  Mr.  Paul  B. 
Sawyer.  He  has  not  only  worked  faithfully  in  taking 
measurements  and  in  constructing  apparatus,  but  he 


TABLE    XIV 

A.    C.    SERIES  SHADE  OPALESCENT    INNER 

LAMP  268 


Angle 

Inters 

ty 

75°  A 

60°  A 

45CA 

30°  A 

15°  A 

98    H. 

U. 

Hor. 

253 

15°  B 

310 

30°  B 

352 

45°  B 

348 

60°  B 

319 

75°  B 

267 

Globes 


E.  M.  F 

Current 

Apparent  watts 

Watts 

Power  factor 

Mean  hemispherical  intensity,  H.  U. 
Watts  per  mean  hemispherical,  H.  U 


Clear  Outer 
Opalescent  Inner 


70  volts 
6.6  amperes 
462. 

397- 
.86 

3i4- 
1.26 


has  offered,  from  time  to  time,  suggestions  of  value. 
I  have  also  had  the  assistance  of  two  members  of 
the  Senior  Class  at  Purdue  University :  Messrs.  P. 
G.  Winter  and  G.  F.  Hardwicke. 

Respectfully  submitted, 

C.    P.    MATTHEWS, 


^S£2^^  — ===== 


jut  10 


50Tn-7,'16 


